题目内容

I haven't seen you since you came back from holiday. ________a nice time？
[A]Do you have
[B]Did you have
[C] Have you had
[D]Had you had

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一般单基因控制的植物雄性不育属于不育。它败育过程发生较，且败育得十分彻底，用常规方法得不到_

It's no use asking the children to keep quiet. They can't help _________noise.
[ A]make
[B]to make
[C]making
[D] made

在涉及某一相对性状的正反交中，F₁均表现其中一个亲本的性状，则该性状的遗传由核基因控制。

嫁接是无性杂交也能实现基因重组，产生新的变异。