It is when the plane ______ that you’d better find out at the booking office. 請問，這個選哪個

這是個強調句. when the plane ______ 是被強調部分, 賓語從句

原句為:

you’d better find out at the booking office when the plane [ is taking off]

妳最好在售票處打聽壹下飛機在什麽時候起飛

可見指的是說話以後的事, 所以選D

進行式表將來

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