问题

They ___________ for two hours
A:is working
B:worked
C:have been working
D:had worked
B:worked
C:have been working
D:had worked
正确答案是:
同类题型
The book is very interesting. I it twice already.
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Rather than ___ on a crowded bus, he always prefers _____ a bicycle
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Did you listen to the speech?— No, we ______ it. But we had a lot of traffic on our way.