Now we can fly to Tokyo. There was a time we had to take a boat.A. howB. whatC. whyD. whe

问题补充：

Now we can fly to Tokyo. There was a time we had to take a boat.

A. how

B. what

C. why

D. when

答案：

A. how

B. what

C. why

(答案→)D. when

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