题目内容

不同组合的不育株与可育株杂交得到以下后代：
写出各杂交组合中父本的遗传组成。

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基因型为rr的左旋椎实螺作母本与Rr的右旋父本交配，F₁代产生右旋和左旋2种个体，且比例各占一半。

玉米条斑叶的遗传是属于母性遗传，而引起条斑性状表现的胞质基因的性质又受有关核基因的控制。

We know from the text that Pete________
[A]was trained to stay at station
[ B ] often plays with food before he eats
[ C ] likes to eat fish without fins
[ D] was smart in teaching the bird a lesson

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