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  Desert plants fall into two sorts according to the way they deal with the problem of surviving drought. There are the drought―avoiders―those which persist（存留） only as seeds, ready to spring up when it rains, to flower quickly and produce another crop of seeds, and to die again. There are also the drought―resisters―those which have evolved various methods for strong water, locating underground water, or reducing their need for water by such devices as shedding their leaves. The drought―resisters are perennials(多年生植物),they manage to live from one rainy season to another, slowly growing bigger and bigger. Of these, the succulents(肉質(zhì)的) is a small but interesting fraction(小部分). They may store water in their leaves, in their stems, or in underground containers.

  In the American deserts the best―known succulents are the cacti(仙人掌). They come in a wide range of sizes, from 50―foot tall giant saguaros(樹形仙人掌) to tiny round cacti about the size of a thumb―nail. They take thick, cylindrical(圓柱體的) or even spherical forms, thereby exposing a minimum of evaporating surface to the air and light. They are leafless, except in youth, and then the leaves are small. Typically their surfaces are spiny, discouraging thirsty animals, and channeled like an accordion(手風(fēng)琴), so the fleshy stem may expand quickly when the plant drinks and contract slowly as it uses up the water. The root system is widespread and shallow, with good reason; only about 3 per cent of the rain that falls on the desert penetrates to any significant depth into soil.

65. The passage classifies（將……分類） the desert plants according to___ .

A. the ways they take to deal with the typical climatic condition in desert

B. their shape

C. how they use water

D. when they produce their seeds

66. According to the passage, some desert plants drop their leaves ___ .

A. because the temperature is too high

B. so that the plants can evaporate less water

C. because they are drought resisters

D. so that the plants can store more water

67. What interests the author most when he or she mentions succulents is that ___ .

A. they take thick cylindrical or even spherical shape

B. they are best―known in America

C. they have many ways of containing water

D. some of them can be very tiny

68. The passage gives us an impression that ___ .

A. the desert plants are shaped in a way as if them were designed by somebody on purpose

B. more water is needed in desert so that more desert plants can grow there

C. more lands will be turned into desert if we do not try harder to save water in our daily life

D. the cacti are the most famous desert plants in America

Desert plants fall into two sorts according to the way they deal with the problem of surviving drought．There are the drought—avoiders—those which persist（存留） only as seeds, ready to spring up when it rains, to flower quickly and produce another crop of seeds, and to die again．There are also the drought—resisters—those which have evolved various methods for strong water, locating underground water, or reducing their need for water by such devices as shedding their leaves．The drought—resisters are perennials(多年生植物),they manage to live from one rainy season to another, slowly growing bigger and bigger．Of these, the succulents(肉質(zhì)的) is a small but interesting fraction(小部分)．They may store water in their leaves, in their stems, or in underground containers．

In the American deserts the best—known succulents are the cacti(仙人掌)．They come in a wide range of sizes, from 50—foot tall giant saguaros(樹形仙人掌) to tiny round cacti about the size of a thumb—nail．They take thick, cylindrical(圓柱體的) or even spherical forms, thereby exposing a minimum of evaporating surface to the air and light．They are leafless, except in youth, and then the leaves are small．Typically their surfaces are spiny, discouraging thirsty animals, and channeled like an accordion(手風(fēng)琴), so the fleshy stem may expand quickly when the plant drinks and contract slowly as it uses up the water．The root system is widespread and shallow, with good reason; only about 3 per cent of the rain that falls on the desert penetrates to any significant depth into soil．

1．The passage classifies（將……分類） the desert plants according to

___ ．

A．the ways they take to deal with the typical climatic condition in desert

B．their shape

C．how they use water

D．when they produce their seeds

2．According to the passage, some desert plants drop their leaves ___ ．

A．because the temperature is too high

B．so that the plants can evaporate less water

C．because they are drought resisters

D．so that the plants can store more water

3．What interests the author most when he or she mentions succulents is that ___ ．

A．they take thick cylindrical or even spherical shape

B．they are best—known in America

C．they have many ways of containing water

D．some of them can be very tiny

4．The passage gives us an impression that ___ ．

A．the desert plants are shaped in a way as if them were designed by somebody on purpose

B．more water is needed in desert so that more desert plants can grow there

C．more lands will be turned into desert if we do not try harder to save water in our daily life

D．the cacti are the most famous desert plants in America