16. Ordinary plants are unable to survive in the desert mainly because of the changeable weather.
A. Right B. Wrong C. Not mentioned
17. Grasses and flowers in desert are able to survive because they stay in the form of seeds to wait for the right amount of water to come.
A. Right B. Wrong C. Not mentioned
18. Grasses and flowers in the desert whose life cycles are short shows their ability to adapt to the quick disappearance of rainwater there after it falls in spring.
A. Right B. Wrong C. Not mentioned
19. Winter is the toughest season for grasses and flowers to survive in desert
A. Right B. Wrong C. Not mentioned
20. The shoot system of perennials can help the plants absorb less of the sun's ray.
A. Right B. Wrong C. Not mentioned
21. The theme of the second last paragraph is why the perennials can survive as plants for several years.
A. Right B. Wrong C. Not mentioned
22. Desert perennials lose their leaves after the rainy season just as trees lose theirs in wetter climates before winter arrives， but the reasons for this feature are different.
A. Right B. Wrong C. Not mentioned
参考答案：
16. B 17. A 18. A 19. C 20. B 21. A 22. B
