问题 选择题

一只果蝇的基因发生突变后,在21℃的气温下生活力很差,在气温上升到25℃时,其生活能力大大提高了.这说明(  )

A.环境条件的变化对变异个体来讲是有利的

B.变异个体的体质增强

C.变异的有利与有害取决于环境条件

D.生物的变异常常是有利的

答案

按照变异对生物是否有利分为有利变异和不利变异.有利变异对生物生存是有利的,不利变异对生物生存是不利的.生物与环境相适应,环境不断变化,因此生物只有不断变异,才能适应不断变化的环境.有的变异对生物个体本身有利,有利于个体生存的变异是有利变异;对个体生存不利的变异是不利变异.一种果蝇的基因发生突变后,产生的变异在21℃的气温下生活能力很差,表明该变异不适于此环境,是不利变异;在气温升高到25℃,其生活能力大大提高了,表明该变异适于25度的环境,在25度的环境中是有利变异.因此变异的有利、有害完全取决于环境条件,适应环境的变异是有利变异.

故选:C.

解答题
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.

20().

A.friends

B.relatives

C.twins

D.brother and sister