Plants in Desert Only specia_考试试题_职称英语

试题来源：职称英语模拟题-理工类-阅读判断
【单选题】

Plants in Desert

Only special plants can survive the terribleclimate of a desert， for these are regions where theannual range of the soil temperature can be over 75℃.Furthermore， during the summer there are few clouds inthe sky to protect plants from the sun's ray. Another problem is the fact thatthere are frequently strong winds which drive small， sharp particles of sand into the plants， tearing anddamaging them. The most difficult problem for all forms of plant life， however， is the fact that the entire annualrainfall occurs during a few days or weeks in spring.

Grasses and flowers in desert survive from oneyear to the next by existing through the long， hot， dry season in the form of seeds. These seeds remain inactive unlessthe right amount of rain falls. If no rain falls， or ifinsufficient rain falls， they wait until the next year， or even still the next. Another factor that helps these plants tosurvive is the fact that their life cycles are short. By the time that thewater from the spring rains disappears —— just a fewweeks after it falls —— such plants no longer need any.

The perennials have special features whichenable them to survive as plants for several years. Thus， nearly all desert perennials have extensive root systems belowground and a small shoot system above ground. The large root network enablesthe plant to absorb as much water as possible in a short time. The small shootsystem， on the other hand， considerably limits water loss by evaporation.

Another feature of many desert perennials isthat after the rainy season they lose their leaves in preparation for the long， dry season， just as trees in wetterclimates lose theirs in preparation for the winter. This reduces their waterloss by evaporation during the dry season. Then， innext rainy season， they come fully alive once more， and grow new branches， leaves and flowers， just as the grasses and flowers in desert do.

16. Ordinary plants are unable to survive inthe desert mainly because of the changeable weather.