问题 选择题

某种农药对杀灭松毛虫有独特的效果,随着使用年限的增长,防治效果越来越差,这是因为有些松毛虫产生了抗药性,产生抗药性变异的原因是(  )

A.松毛虫的适应能力强

B.农药诱导松毛虫产生抗药性

C.农药使松毛虫产生了隔离

D.环境选择积累了松毛虫的抗药性

答案

答案:D

题目分析:达尔文把在生存斗争中,适者生存、不适者被淘汰的过程叫做自然选择,遗传变异是生物进化的基础,首先松毛虫的抗药性存在着变异,有的抗药性强,有的抗药性弱,使用农药时,把抗药性弱的细菌杀死,这叫不适者被淘汰,抗药性强的松毛虫活下来,这叫适者生存,活下来的抗药性强的松毛虫,繁殖的后代有的抗药性强,有的抗药性弱,在使用农药时,又把抗药性弱的松毛虫杀死,抗药性强的松毛虫活下来,这样经过若干代的反复选择,最终活下来的松毛虫大多是能抵抗农药的松毛虫,使得有些松毛虫不再受青霉素影响了,故选D。

单项选择题

This was one of my experiences (1) . When I was in my 30s, I was working for a large international company which had its head office in London. I was working in the (2) department.

The company had a training centre which was just outside London. Different courses were held there throughout (3) and I (4) go on one training course a year. These usually started (5) a Sunday evening and lasted six days.

Once I was (6) a week’s training course with about forty (7) sales people. I was in the bar on the Friday evening and suddenly a woman who was (8) behind the bar asked mea curious question. "I hope you don’t (9) my asking," she said, "but I’ve been (10) about it all week. Have you got a sister (11) Mary" The woman’s name was June. And she used to do various jobs at the training centre. She worked in the office, she organized all the food and drink for the centre and she worked in the bar at lunchtime and in the evening.

My answer (12) June’s question was "Yes", and June said, "I thought (13) . I met her last September when she was organizing a course here. " At that time, my sister was working for (14) company but in a different part of the country. That was (15) she came to be at the training centre.

(16) surprised me was how June guessed we were brother and sister. Three things made it even more (17) . First, she had met my sister six months before she met me. Second, they have about sixty new people every week at the training centre. So about one thousand five hundred people had (18) the centre in those six months. And (19) , my sister is married, so she doesn’t have the same family name as me.

We’re not (20) , but I guess we must look quite like each other.

11().

A.called

B.calling

C.calling on

D.calling up

单项选择题