题干

下图表示培育高品质小麦的几种方法,下列叙述正确的是(   )


A:图中涉及的育种方法有杂交育种、单倍体育种和诱变育种

B:a过程能提高突变频率,从而明显缩短育种年限

C:a、c过程都需要用秋水仙素处理萌发的种子

D:要获得yyRR,b过程需要进行不断自交来提高纯合率

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答案(点此获取答案解析)

A,D

同类题4

阅读理解

    What is the difference between developed and developing countries? The question is quite a difficult one. But we can compare them in two important aspects: people and economy.

    In developing countries there are high rates of both birth and death. Families decide to give birth to more than one child, because many developing countries do not have the systems necessary to guarantee(保证) the life of old people. Raising more children seems to be the only way to make sure that during their later years a person will be taken care of.

    The situation is completely different in fully-developed countries. Those countries have low levels of birth and mortality. Low mortality rate is mainly because of the good health care, but low birth rate is due to the fact that supporting a family with more children is expensive nowadays. Another reason is that more and more women decide to work outside, so there is usually no time and place for a large group of children in their lives.

    In developed countries, most industries have high levels of technological progress, while in developing countries most GDP comes from agriculture. It is mainly due to the fact that services and many branches of industry are in the stage of development. But they have the potential to develop quickly, because they have many things to improve.

    Of course, the difference between developed and developing countries is not that clear, because some countries might be in the middle of great changes. When a country is in that stage, some data can define the country as a developing one, but others may show that it is a developed one.