问题 选择题

蝗虫身体表面有坚硬的外骨骼,其主要作用是

A.防止体内水分散失

B.控制身体生长的速度

C.扩大活动范围

D.对寻找食物和配偶有利

答案

答案:A

题目分析:昆虫的体表具有坚硬的外骨骼,其主要作用是保护和支持内部的柔软器官、防止体内水分的蒸发散失,这是适应陆地生活的特点之一,外骨骼不能随着昆虫身体的生长而长大,所以在金蝉的生长发育过程中,有脱掉原来的外骨骼的现象,这就是蜕皮,选A。

单项选择题
单项选择题

Most plants can make their own food from sunlight, (1) some have discovered that stealing is an easier way to live. Thousands of plant species get by (2) photosynthesizing, and over 400 of these species seem to live by pilfering sugars from an underground (3) of fungi(真菌). But in (4) a handful of these plants has this modus operandi been traced to a relatively obscure fungus. To find out how (5) are (6) , mycologist Martin Bidartondo of the University of California at Berkeley and his team looked in their roots. What they found were (7) of a common type of fungus, so (8) that it is found in nearly 70 percent of all plants. The presence of this common fungus in these plants not only (9) at how they survive, says Bidartondo, but also suggests that many ordinary plants might prosper from a little looting, too.

Plants have (10) relations to get what they need to survive. Normal, (11) plants can make their own carbohydrates through photosynthesis, but they still need minerals. Most plants have (12) a symbiotic relationship with a (13) network of what are called my corrhizal fungi, which lies beneath the forest (14) . The fungi help green plants absorb minerals through their roots, and (15) , the plants normally (16) the fungi with sugars, or carbon with a number of plants sharing the same fungal web, it was perhaps (17) that a few cheaters—dubbed epiparasites—would evolve to beat the system. (18) , these plants reversed the flow of carbon, (19) it into their roots from the fungi (20) releasing it as "payment.\

7()

A.evidences

B.pictures

C.traces

D.tracks