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问题 单项选择题

缺乏细胞壁的原核细胞型微生物是

A．衣原体
B．病毒
C．支原体
D．螺旋体
E．真菌

答案

参考答案：C

解析：原核细胞型微生物包括细菌、螺旋体、放线菌、衣原体、立克次体及支原体，其中仅支原体缺乏细胞壁结构。支原体是原核细胞型微生物中最小的，直径仅0.2～0.3微米 (μm)，最外层即为细胞膜。

选择题

一般来说，愈向食物链后端     

A．生物体的总数量愈多

B．生物体的总质量愈大

C．生物体的总能量愈少

D．生物体的个体愈小
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单项选择题

It is difficult to imagine what life would be like without memory. The meanings of thousands of everyday perceptions, the bases (51) the decisions we make, an d the roots of our habits and skills are to be (52) in our past experiences, which are brought into the present (53) memory.

Memory can be defined as the capacity to keep (54) available for later use. It includes not only "remembering" things like arithmetic or historical facts, but also any change in the way an animal typically behaves. Memory is (55) when a rat gives up eating grain because he has sniffed something suspicious in the grain pile. Memory is also involved when a six-year-old child learns to swing a baseball bat.

Memory (56) not only in humans and animals but also in some physical objects and machines. Computers, for example, contain devices for storing data for later use. It is interesting to compare the memory-storage capacity of a computer (57) that of a human being. The instant-access memory of a large computer may hold up to 100000 "words" —ready for (58) use. An average American teenager probably recognizes the meanings of about 100000 words of English. However, this is but a fraction of the total (59) of information which the teenager has stored. Consider, for example, the number of facts and places that the teenager can recognize on sight. The use of words is the basis of the advanced problem-solving intelligence of human beings. A large part of a person’s memory is in terms of words and (60) of words.

59().

A. deal

B. number

C. mount

D. amount
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