问题 选择题

下列有关性染色体的说法不正确的是(  )

A.人类的性染色体是X染色体和Y染色体

B.X是女性的性染色体,Y是男性的性染色体

C.女性的性染色体组成是XX,男性的性染色体组成是XY

D.X染色体大,Y染色体小

答案

男、女体细胞中都有23对染色体,有22对染色体的形态、大小男女的基本相同,叫常染色体,第23对染色体在形态、大小上存在着明显差异,这对染色体与人的性别决定有关,称为性染色体;人的性别主要是由性染色体决定的,女性体细胞中的性染色体形态大小基本相同,称为XX染色体,男性体细胞的性染色体中,较大的一条命名为X染色体,较小一条称为Y染色体.可见B符合题意.

故选:B

单项选择题 共用题干题
阅读理解

The energy crisis has made people aware of how the careless use of the earth’s energy has brought the whole world to the edge of disaster. The over-development of motor transport, with its increase of more cars, more traveling, has contributed to the near-destruction of our cities and the pollution not only of local air but also of the earth’s atmosphere.

Our present situation is unlike natural disasters of the past. Worldwide energy use has brought us to a state where long-range planning is vital. What we need is not a continuation of our present serious state, which endangers the future of our country, our children, and our earth, but a movement forward in order to work rapidly and effectively on planetary problems.

This country has been failing back under the continuing exposures of loss of morality and the revelation(揭露) that lawbreaking has reached into the highest place in the land. There is a strong demand for morality to turn for the better and for some devotion that is vast enough and yet personal enough to enlist the devotion of all. In the past it has been only in a way in defense of their own country and their own benefits that people have been able to devote themselves wholeheartedly.

This is the first time that we have been asked to defend ourselves and what we hold dear in cooperation with all the other people of this planet, who share with us the same endangered air and the same endangered oceans. There is a common need to reassess our present course, to change that course and to employ new methods through which the world can survive. This is a priceless opportunity.

To grasp it, we need a widespread understanding of nature if the crisis we and the world are facing is no passing inconvenience, no byproduct of the ambitions of the oil-producing countries, no environmentalists’ only fears, no byproduct of any present system of government. What we face is the result of the invention of the last four hundred years. What we need is a transformed life style. This new life style can flow directly from science and technology, but its acceptance depends on a sincere devotion to finding a higher quality of life for the world’s children and future generation.

小题1:Which of the following has nearly destroyed our cities?

A.The loss of beliefs and ideas.

B.More of law-breaking.

C.Natural disasters in many areas.

D.The rapid growth of motors.小题2:By comparing past problems with present ones, the author draws our attention to the        .

A.seriousness of this crisis

B.ineffectiveness of laws

C.similarity of the past to the present

D.hopelessness of the situation小题3:Which of the following is used as an example to show the loss of morality?

A.Disregard for law.

B.Lack of devotion.

C.Lack of understanding.

D.Destruction of cities.小题4:The author wrote the passage in order to        .

A.make a recommendation for a transformed life style

B.limit ambitions of the people of the whole world

C.demand devotion to nature and future generation

D.encourage awareness of the decline of morality