试题出自试卷《宁波大学2011年考博英语真题及答案解析》

Apart from the Moon and occasional comets and asteroids, Venus is often our nearest neighbor. Its orbit brings it closer to Earth than any other planet—only 26 million miles away at certain times. Despite that proximity, for a long time it was generally termed “the planet of mystery.” This is because the atmosphere of Venus is so dense and so cloud-laded that its surface is permanently hidden from sight.
The first attempt to learn more about Venus was to analyze its upper atmosphere using spectroscopic methods. In size and mass, Venus is almost the equal of Earth, and its gravitational field is only slightly weaker than ours, so that logically it might be expected to have the same kind of atmosphere—but this is emphatically not so. Scientists found that the main constituent of its atmosphere is carbon dioxide. Since this is a heavy gas that would be expected to sink, it was reasonable to assume that carbon dioxide made up most of the atmosphere down to ground level. Carbon dioxide acts in the manner of a greenhouse, trapping the Sun’s heat, so it followed that Venus was likely to be a very torrid sort of world.
Yet opinions differed. According to one theory, the clouds contained a great deal of water. It was even claimed that the surface might be largely ocean covered, in which case: the atmosphere carbon dioxide would have fouled the water and produced seas of soda water. Another intriguing theory made Venus very similar to the Earth of over 200 million years ago. There would be marshes, luxuriant vegetation of the fern and horsetail variety, and primitive life-forms such as giant dragonflies. If so, then Venus might presumably evolve the same way Earth has done.
In 1962 the American probe Mariner 2 bypassed Venus at less than 22,000 miles and gave us our first reliable information. The surface proved to be very hot indeed; we now know that the maximum temperature is almost 500°C. The atmosphere really is almost pure carbon dioxide, and those shining clouds are rich in sulfuric acid. All ideas of a pleasant, oceanic Venus had to be abandoned. In 1975 Venera 9, a Russian automatic lander, visited Venus and sent back pictures directly from the surface. The scene—a rocky, scorched landscape—could hardly be more hostile. Subsequent probes have confirmed this impression.
Why is Venus so unlike Earth? The answer can only lie in its lesser distance from the Sun. It seems that in the early days of the solar system the Sun was less luminous than it is now, in which case Venus and Earth may have started to evolve along the same lines, but when the Sun became more powerful the whole situation changed. Earth, at 93 million miles, was just out of harm’s way, but Venus, at 67 million, was not. The water in oceans vaporized, the carbonates were driven out of the rocks, and in a relatively short time or the cosmic scale, Venus was transformed from a potentially life-bearing world into the inferno of today.
25. The primary purpose of this passage is to ______.
26. The statement “In size ... so” (bold in Paragraph 2) functions primarily to ______.
27. The primary purpose of the third paragraph is to ______.
28. In order for the hypothesis in “There would ... dragonflies” (bold in Paragraph 3) to be correct, which statement could NOT be true of conditions on Venus?
29. The statement in “In 1962 … information” (bold in Paragraph 4) suggests that the ______.
30. The tone of the statement in “The answer ... Sun” (bold in Paragraph 5) is best described as ______.