问题

Jack, do you know the answer ______ this question It’s too difficult for me.— Sorry, I don’t know. You can ask Jim for help. He is good at math.

A:stays
B:stayed
C:to stay
D:staying;

正确答案是：

同类题型

Before stamps, people didn’t for the letters they sent,but for the letters they received.

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Elbert Einstein, for ______ life had once been very hard, was successful later in science .

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