Complete Reading Comprehension Test

Passage:
Thunderstorm activity is associated with the vertical motion of warm, unstable air and the formation of cumulonimbus clouds that generate heavy rainfall, thunder, lightning, and occasionally hail (precipitation in the form of ice pellets). At any given time there are an estimated 2,000 thunderstorms in progress over the face of Earth.

As might be expected, the greatest proportion occurs in the tropics, where warm, plentiful moisture, and atmospheric instability are always present. About 45,000 thunderstorms take place each day, and more than 16 million occur each year around the world. Annually the United States experiences about 100,000 thunderstorms and millions of lightning strikes. Thunderstorms are most frequent in Florida and the nearly eastern Gulf Coast region (with activity recorded on 70 to 100 days each year) and in the mountains of New Mexico (50 to 60 days), while the western margin of the United States has the least activity (5 to 20 days).

All thunderstorms require warm, moist air, which, when lifted, will release sufficient latent heat to provide the rising power, or buoyancy, necessary to maintain its upward movement. Although this instability and associated buoyancy are triggered by a number of different processes, all thunderstorms have a similar life cycle. Because instability and buoyancy are enhanced by high temperatures at ground level, thunderstorms are most common in the afternoon and evening. However, surface heating alone is not sufficient for the growth of towering cumulonimbus clouds. The development of cumulonimbus towers also requires a continual supply of moist air. Each new surge of warm air rises higher than the last, adding to the height of these clouds. These updrafts must occasionally reach speeds of over 100 kilometers per hour to accommodate the size of hailstones they are capable of carrying upward. Usually, within an hour the quantity of precipitation particles that has accumulated in a cumulonimbus cloud is too much for the updrafts to support, and in one part of the cloud, downwards develop, releasing heavy precipitation. This represents the most active stage of the thunderstorm.

Passage:
Although Italy is associated with the highest level of artistic innovation in fifteenth- and sixteenth-century Europe, perhaps the most important technical change in Italian painting during this period—the adoption of oil painting—did not originate in Italy. The first reference to mixing pigments with oil comes from an arts manual produced by Theophilus Presbyter (approximately 1070–1125). Walnut or linseed oil was used, and it took an unconscionably long time to dry, as Theophilus complained. The Norwegians used it in the thirteenth century for decoration on wooden objects in churches, including statues and altars. The Italian painter Cennini, in the fourteenth century, saw it as a German method.

It was the painters in the Low Countries (modern Netherlands and Belgium) who took it up in a highly professional way and improved on the process steadily. By the fifteenth century it was their usual method of painting on wooden boards or panels, and they were beginning to use it on walls. They quickly discovered that if they were careful and applied successive layers of thin oil paint, they could achieve effects of great translucency and depth, as with stained (colored) glass. Indeed, the early oil painters were often glass artists too and learned how to achieve the same glowing effects of church windows on nontransparent wood surfaces. Dutch painter Jan van Eyck (who worked between 1422–1441) achieved results that staggered visitors who had never seen oil employed as an art medium—detail, brilliance, sensitivity, great depth, and completely new ways of depicting the existence and fall of light. The biographer Giorgio Vasari, writing a hundred years later, was so impressed by van Eyck’s mastery of the medium that he wrongly credited him with inventing it.

However, painting in oil took a long time to reach Italy and even longer to be generally adopted. Antonello da Messina, a much-traveled painter, is generally credited with being the first Italian to take it up, and he certainly showed some awareness of oil painting during a visit to Venice in 1475–1476. In central Italy, Pietro Vannucci was using mixtures of oil and tempera (water-based paint) in the 1480s. Venice was the first Italian city to adopt oil enthusiastically, and the adoption had lasting effects. It is certainly not true that the Venetians paid little attention to drawing and line as before applying paint to it, but they were never as devoted to drawing as the artists of Florence were; once they had adopted oil with such passion it was oil paints allowed them to change their minds while working on a painting. X-rays of paintings not originally seen as oil paintings (known as pentimenti), thereby revealing an artist’s earlier versions of a painting. X-rays of Venetian painter Giorgione’s masterpiece, The Tempest, which may be from as early as 1505, reveal that Giorgione replaced a sitting female figure with the image of a standing soldier in the final version. The Venetians also achieved richer and subtler effects with oil, and allowed for dramatic contrasting effects of darkness and light. Hence, just as the Florentines were prominent for their skill in drawing, the Venetians attained an unrivaled reputation for color and drama.

There were other, equally fundamental consequences. If the artists of the Low Countries initially painted in oils on wood, they soon also learned to use stretched canvases made of linen cloth, variously treated to receive oil paint. The introduction of canvas was almost as important as the use of oil, for it gave artists much more freedom in determining the size, shape, and texture of their working surface, adding lightness and economy too. Painting on stationary wooden wall panels, a practice that went back a long time, was succeeded or complemented by a new and revolutionary painting on an easel, a portable, temporary stand for holding a canvas. Once artists could make a living from painting smallish canvases or panels on an easel, they could paint portraits, too, as now one of the most profitable art forms. The artist could either carry the easel about from place to place or work from a studio, where the painter could readily get models to sit for a painting.

Passage:
Animals of the same species fight in their competition for resources, but they also help one another. From an evolutionary perspective, helping can be defined as any behavior that increases the survival chance or reproductive capacity of another individual. Given this definition, it is useful to distinguish between two categories of helping—cooperation and altruism.

Cooperation occurs when an individual helps another while, at the same time, helping itself. This sort of helping occurs all the time in the animal world. It occurs when a mated pair of foxes work together to raise their mutual young or a troop of macaque monkeys work together to repel another troop. Most of the advantages of social living lie in cooperation. By working with others for common ends, each individual has a better chance of survival and reproduction than it would have outside the social group. There is nothing about cooperation that negates Darwin’s theory of the survival of the fittest. It is selfish. It is a way of obtaining resources that one cannot obtain alone. Whatever costs accrue are more than repaid by the benefits.

Altruism, in contrast, occurs when an individual helps another while, at the same time, decreasing its own survival chance or reproductive capacity. Animals do sometimes behave in ways that at least appear to be altruistic. For example, some animals, including female ground squirrels, emit a loud, distinctive call when they spot an approaching predator. The call warns others of the predator’s approach and at the same time tends to attract the predator’s attention to the caller. The selfish response would be to remain quiet and hidden rather than risk one’s own death by warning others. How can such behavior be explained from an evolutionary perspective? Any evolutionary account of apparent altruism must operate by showing that from a broader perspective the behavior is not truly altruistic. Sociobiologists have developed two broad theories to account for apparent acts of altruism in animals—the kin selection theory, holding that such acts of altruism come about because they are most likely to help close relatives, and the reciprocity theory, arguing that acts of altruism occur because they increase the chances of receiving help from others in the future.

Passage:
Grains, notably wheat, provide a substantial part of Canada’s agricultural revenue. Cultivation is concentrated in the prairie provinces of Alberta, Manitoba, and Saskatchewan. A special variety of wheat—Marquis—was developed to withstand the country’s dry climate and short growing season, and the wheat economy boomed with the coming of the railroads in the late 1800s. Rapid transportation to eastern ports opened access to world markets, and large grain elevators were built to store grain beside the rail lines.

A system of “dryland farming,” first introduced into the prairies in the 1880s, facilitated the spread of large-scale cereal farming. It involves the systematic use of “summer fallow” to limit the effects of low annual rainfall. Once a crop has been harvested, the land is left crop-free for a year so that it can store moisture and yield a good crop the next year.

The adoption of dry farming methods, as well as the introduction of fast-maturing grain varieties, helped Canadian farmers to greatly increase the area of land under cultivation in the first three decades of the twentieth century. Although dryland farming gradually reduces soil fertility over a long period of time, this can be forestalled by the use of fertilizers, and the system is still widely used as a means of conserving moisture.

Wheat still dominates wheat farming in the prairies, except in the driest areas where it has been replaced with cattle ranching. Between 1900 and 1930 the area under wheat cultivation rose from 610,000 hectares to 10 million hectares. This phenomenal expansion was halted during the 1930s by drought and world economic depression, and subsequently by the disruption of the Second World War. But by the 1950s, production and exports were again increasing. Long-term contracts to supply wheat to China and the Soviet Union opened up new markets in addition to the traditional ones in Britain and Japan. The 1960s saw an expansion of beef production in the region at the expense of some wheat production, but since then higher grain prices have led to a new resurgence in wheat growing, and by the 1990s grains overtook livestock as the largest single source of revenue in the Canadian agricultural economy.