2015年1月25日托福阅读真题P3+题目+答案：Preventing Overgrowth among Tree Branches

2015年1月25日托福阅读真题P3+题目+答案：Preventing Overgrowth among Tree Branches

One way trees prevent themselves from having too many braches is simply by shedding (dropping off) branches once they have fulfilled their purpose. This happens as the tree gets bigger and grows new outer layers of foliage that shade the inner and lower branches. In most large trees, the center of the canopy contains only large branches, small branches and fine twigs are found only at the canopy’s edge. In the shaded center, the small branches that would once have occupied that space are long gone. Trees like the true cypresses regularly shed small twigs complete with leaves toward the end of summer. Most other trees shed only branches that prove unproductive. If a branch is not producing enough carbohydrate to cover its own running costs—i.e., it needs to be subsidized by other branches because, for example, it is being shaded and receives little light—it will usually be got rid of. This prevents unproductive branches from being a drain on the tree and removes the wind drag (the force of air resistance) from useless branches.

24. All of the following situations are mentioned in paragraph 1 for a tree to shed its branches EXCEPT

A endangering other branches

B building up on a tree

C wasting a tree’s resources

D growing larger

25. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

A.A tree will usually shed branches that use more carbohydrate than they produce.

B. Branches that are shaded usually do not receive enough light to produce all the carbohydrate they need.

C. If a tree gets rid of a branch, it is usually because other branches lack enough carbohydrate to subsidize it.

D. If a branch is shaded and cannot produce as much carbohydrate as it needs, it will usually be subsidized by other branches.

26. According to paragraph 1 most twigs of the true cypresses would be arranged in which of the following manner

A. Most small twigs on true cypresses have been found located at the margins of the canopy.

B. The shaded center areas of true cypresses are generally occupied by many small twigs and branches.

C. True cypresses shed twigs that grow on large, unproductive branches.

D. True cypresses seasonally shed small twigs without regard to whether they are productive or not.

Branches are shed for reasons other than lack of light. In dry parts of the world, it is common for trees and shrubs to lose smaller branches to save water. Small branches have the thinnest bark (the protective outer covering of a tree) and greatest surface area and thus are the source of most water loss once the leaves have been lost. The creosote bush of United States deserts self-prunes, or removes parts of itself, in the face of extreme heat or drought, starting from the highest and most exposed twigs and working downward to bigger and bigger branches, it’s a desperate act because if the creosote bush loses too much food, it dies. Shedding branches can also be useful for self-propagation. Most poplar trees and willow trees characteristic of waterways will readily drop branches, which take root when washed up on muddy banks further downstream.

27. Which of the following best describes the role of the explanation offered in paragraph 2?

A Paragraph 2 questions this explanation by providing counterexamples of some trees.

B Paragraph 2 presents additional evidence supporting this explanation.

C Paragraph 2 discusses some additional reasons why trees shed branches

D Paragraph 2 points out some additional consequences for trees besides the shedding of branches

28. The word “exposed” in the passage is closet in meaning to

A distant

B unprotected

C easily replaced

D unproductive

29. According to paragraph 2, what is true of the creosote bush of United States deserts?

A It tends to grow small branches during dry parts of the year.

B It loses more water through its bark than through its leaves.

C It loses its lower branches only after losing upper ones.

D It sheds branches for the purpose of propagating itself.

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