问题 选择题

果蝇的眼色由一对等位基因(A、a)控制。在纯种暗红眼♀×纯种朱红眼♂的正交实验中,F1只有暗红眼;在纯种朱红眼♀×纯种暗红眼♂的反交实验中,F1雌性为暗红眼,雄性为朱红眼。则下列说法不正确的是[ ]

A.正、反交实验常被用于判断有关基因所在的染色体类型

B.反交的实验结果说明这对控制眼色的基因不在常染色体上

C.正、反交的子代中,雌性果蝇的基因型都是XAXa

D.若正、反交的F1中雌、雄果蝇自由交配,其后代表现型的比例都是1:1:1:1

答案

答案:D

计算题
阅读理解

Many facts suggest that children are overweight and the situation is getting worse,according to the doctors.I feel there are a number of reasons for this.

Some people blame the fact that we are surrounded(包围)by shops selling unhealthy,fatty foods,such as fried chicken and ice cream,at low prices.This has turned out a whole generation of grown-ups who seldom cook a meal for themselves.If there were fewer of these restaurants,then probably children would buy less take-away food.

There is another argument that blames parents for allowing their children to become overweight.I agree with this,because good eating habits begin early in life,long before children start to visit fast food shops.If children are given fried chicken and chocolate rather than healthy food,or are always allowed to choose what they eat,they will go for sweet and salty foods every time,and this will carry on throughout their lives.

There is a third reason for this situation.Children these days take very little exercise.They do not walk to school.When they get home,they sit in front of the television or their computers and play computer games.Not only is this an unhealthy pastime(消遣),it also gives them time to eat more unhealthy food.What they need is to go outside and play active games or sports.

The above are the main reasons for this problem,and therefore we have to encourage young people to be more active,as well as steering them away from fast food shops and bad eating habits.

小题1:According to the text,what kind of children may eat more unhealthy food?

A.Those who often take exercise.

B.Those who often watch television.

C.Those who often have meals at home.

D.Those who often walk to school.小题2:The author thinks that children are becoming overweight because ________.

A.their parents often cook meals for them

B.they are too busy to go out and play

C.they can’t choose what to eat

D.there are too many fast food shops around小题3:The word“steering”underlined in the last sentence most probably means ________.

A.forcing

B.guiding

C.driving

D.moving小题4:The main purpose of the text is to ________.

A.tell a story

B.provide facts

C.give advice

D.compare opinions