问题 单项选择题

艾滋病被称为“20世纪的瘟疫”,艾滋病病毒将人体内的()作为攻击目标。

A.红细胞

B.血红蛋白

C.淋巴细胞

D.神经系统

答案

参考答案:C

解析:

HIV病毒为逆转录病毒,该病毒能结合人类具有CD4+受体的细胞,特别是和CD4T辅助淋巴细胞相结合,还能与神经细胞表面的半乳糖神经酰胺结合,逆转录酶可将病毒RNA逆转录为DNA,然后DNA再与人类基因相整合。病毒DNA序列被感染细胞及其子代细胞终身携带。故选C。

单项选择题
阅读理解

Can hard work be replaced by machines in agriculture? Yes, man is trying out automatic (自动化) farming. It is fun to watch a machine picking tomatoes. The strange machine sails like a ship across a sea of plants. In its front is a hole. As the machine moves forward, tomato plants are pulled into the hole. The tomatoes are gathered while the rest of the plants are thrown back onto the fields.  Twelve workers sit on top of the machine. They rapidly pick out the bad fruit from the tomatoes. A red stream of ripe tomatoes is being sent into a cart that is pulled alongside the machine. One driver and twelve workers can pick in an hour ten tons of a new kind of tomato. Without the invention, it would take 60 men to do the job.

Not all plants cooperate well with the farming machines. Take lettuce(莴苣)for example, seeds plants in the same field in the same time ripe at different times. The only way to tell a ripe head of lettuce is to look at it and feel it. And now there is a machine even to do that!

There is a special machine to test lettuce. When it moves over one that feels right, it sends a signal back to the picking machine which goes behind. The cutting and picking is done satisfactorily by this unit.

64.This passage mainly tells us something about        .

A.the machines picking tomatoes      B.automatic farming

C.the science of farming     D.agriculture machines 

65.After the bad tomatoes are picked out,        .

A.the others are sent into a cart nearby

B.the workers carry them away

C.the others are put into bags

D.the others will be thrown into the field

66.The last paragraph mainly tells us          .

A.that lettuce is not good to get in

B.that a special unit of machines has been made to test and pick lettuce

C.about a wonderful machine that can be used pick all kinds of plants

D.that lettuce is not a cooperation plant