问题 选择题

下列现象中,属于可遗传的变异的是                                  (     )

A.同卵双生的姐妹胖瘦不同

B.人的镰刀型细胞贫血症

C.父母都能卷舌,孩子不能卷舌

D.某人用眼不当导致近视

答案

BC

题目分析:遗传是指亲子间的相似性,变异是指子代与亲代之间的差异,子代个体之间的差异的现象.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.按照变异的原因可以分为可遗传的变异和不遗传的变异.可遗传的变异是由遗传物质改变引起的,可以遗传给后代;由环境改变引起的变异,是不遗传的变异,不能遗传给后代.

A.同卵双生的姐妹胖瘦不同是环境改变引起的变异,遗传物质没有改变,是不可遗传的变异;

B.人的镰刀型细胞贫血症,遗传物质发生了改变,是可遗传的变异;

C.父母都能卷舌,孩子不能卷舌,遗传物质发生了改变,是可遗传的变异;

D.某人用眼不当导致近视,是环境改变引起的变异,遗传物质没有改变,是不可遗传的变异;

阅读理解

阅读理解。|

     根据短文内容,从短文后的选项中选出能填入空白处的最佳选项,选项中有两项为多余选项。

     The person behind you constantly kicks the back of your seat. Your talkative seatmate doesn't

understand your need for sleep. And the aircraft's bathroom is a total mess, These situations can make

even a short flight unbearable . Hopefully you don't cause these unpleasant experiences for others.  1  .

Always recline(向后倾斜) your seat slowly. There's nothing worse than suddenly being hit in the knees

by the seat in front of you. In addition, don't keep your seat reclined for the entire flight. Always keep it

upright during mealtimes. And remember to put it in the upright position before going to the restroom (or

anytime you leave your seat. )

        2  Wait until the meal is done and all the food trays(盘子) have been collected . It's hard for

passengers to stand up to let you pass when they still have their food trays. And when using the bathroom ,always clean up after yourself-the next user will be grateful !

Keep your body-and your possessions-to yourself as much as possible so as not to crowd your in-flight

seatmate(s) . Share the armrest , especially on a long flight . Also, be careful not to kick or push on the

seat in front of you.

While some people enjoy chatting with other passengers during a flight, not everyone does. Some people may want to nap ,read or work.  3  

If you are traveling with someone and want to chat, keep your voices low,   4   People can still hear

through your headphones if the volume is too high.

When exiting the plane, if others are having trouble with their carry-on luggage . help them if you can. If

you can't help ,wait patiently, and don't push past people to get off the airplane. On your flight , remember

the golden rule:   5  .

A. Don't leave your carry-on in the aircraft.

B. If the conversation seems one-sided , you should notice it.

C. Treat others the way you want to be treated!

D. Avoid going to the bathroom during mealtimes.

E. Instead ,you can set an example by following these common airplane courtesies(礼貌)

F. It is not polite to talk loudly in the aircraft.

G. If using electronic gadgets(小装置),keep the volume down.

单项选择题