题干

诱变育种有很多突出优点,也存在一些缺点,下列分析正确的是(   )
①结实率低,发育迟缓     ②提高变异频率,使后代变异性状较快稳定,因而加快育种进程     ③大幅度改良某些性状    ④茎杆粗壮,果实种子大,营养物质含量高 
⑤有利个体不多,需要大量的材料

A:①④  

B:②③⑤

C:①④⑤ 

D:①②④

上一题 下一题 0.0难度 选择题 更新时间:2014-12-10 10:55:57

答案(点此获取答案解析)

B

同类题4

阅读理解

    Before I had my son, I spent two years working with children with disabilities. I learnt that shouting and threats of punishment would result in a disaster. Coming up against their behaviour could only make the job harder and their behaviour more extreme. I found something that worked, though.

    There was a very naughty boy in the nursery and a teacher who was generally very confident with the children was asked to take charge of him. One day the boy joined a session in the room next to mine. His appearance created an atmosphere of tension. He spent the entire session running around, hitting and kicking, and destroying property.

    I was in the craft room working with some other children when my co­worker told me that this boy's teacher was in tears, and could not get control of the situation. As we were talking, the boy ran in. I told my co­worker that I would take care of him.

    I closed the door. He was full of energy, throwing things around and making a huge mess. But I could see that he was doing all these to annoy me. He needed connection, and this was the only way he knew how to ask for it. So I sat back down and kept quiet. Then he slowed down and began making a rocket. I talked to him about it. We continued like this for a few minutes before I slipped into the conversation:

    “So what happened today?”

    It was purely a question, no blame or anger in my tone. I believe that if I had criticized him, the gate that was slowly opening would have shut firmly closed. He told me that the teacher didn't let him do what he knew well due to safety but asked him to do what he disliked. He also admitted that he had enjoyed making her run around and saw it as a game. I explained that his teacher had not seen it as a game and was very upset. This again was stated simply as a fact. I suggested that next time he had a session, he talk about what he hoped to do at the start, which might be easier for everyone. He agreed and was quiet for a moment. Then he looked at me with tears in his eyes before quietly asking if he could go to find his teacher to apologize.