问题补充：
It is when the plane that you’d better find out at the booking office.
A. would take off
B. had taken off
C. was taking off
D. is taking off
答案：
A. would take off
B. had taken off
C. was taking off
(答案→)D. is taking off
解析：注意题干为强调句型。take off用进行时态表示将来。
