题干

关于基因突变的下列叙述中,错误的是

A:基因突变是指基因结构中碱基对的增添、缺失或改变

B:基因突变是由于基因中脱氧核苷酸的种类、数量和排列顺序的改变而发生的

C:基因突变可以在一定外界环境条件或者生物内部因素的作用下引起

D:基因突变的突变率是很低的,并且都是有害的

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D

同类题2

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    From: Wendy and Jack Brown

    Date: September 22, 2014

    To: 8th and 9th graders at R.L.S. Junior School

    Subject: Bonjour!

    Bonjour! (That means hello in French.)

    We hope you all had a great summer. Ours was a lot of fun. We have seen so many new things and met so many wonderful people. The French gave us a warm welcome and helped us get used to living here soon. We have so many things to share with all of you. We are going to send you more emails, but here are the best parts of our holiday in France so far.

    We had a fantastic time seeing the Tour de France this summer. It is the most famous bicycle race in the world. The riders travel more than two thousand miles in about a month! We got a quick look at the riders as they sped past! After the race, our family rented bikes, and rode along part of the route that the cyclists used.

    A few of you asked whether the French really eat snails(蜗牛). The answer is yes. We went out to dinner the other day, and our parents ordered some. We each tried one and it didn't taste too bad. The snails, called escargots, are served with lots of butter. They feel a little rubbery when you bite into them, but they don't really have much taste. Mum's favourite food here is the French pastries. Dad loves the red wine. Our favourite is the fresh bread from the shop down the street.

    We went to visit the Eiffel Tower a few weeks ago. We went all the way to the top. It was a sunny day, so we could see for miles and miles into the distance. Dad doesn't like heights, so he stayed at the bottom of the tower and took pictures from the ground.

    We miss all of you a lot. Write back to us and let us know what is new at home.

Au revoir! (Can you guess what that means in French?)

Wendy and Jack Brown