题目内容

嫁接是无性杂交也能实现基因重组，产生新的变异。

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We know from the text that at Yellowstone_________.
[ A] temperatures can go from o t0 80 degrees
[B] it snows throughout the year except for summer
[C] thunderstorms can be seen throughout the year
[D]it is more windy and rainy illthe spring

一个品种的花粉授到不育系上，F₁正常散粉可育；而另一个品种的花粉授到该不育系上，F₁所有个体均不育。那么前一个品种是这个不育系的，基因型可表示为；后一个品种则是这个不育系的，基因型可表示为。该不育系是属于__类型的不育。

We learn from the text that raccoons _ .
[ A] only come out at night
[ B] often visit people ' s houses
[ C] like to find food in rubbish cans
[ D ] like to live with people in winter

[A] calculation
[B] average
[C] estimate
[D] total