问题补充：
Ladies and gentlemen, please fasten your seat belts .The plane .
A. takes off
B. is taking off
C. has taken off
D. took off
答案：
A. takes off
(答案→)B. is taking off
C. has taken off
D. took off
解析：考查时态：句意是：先生们女士们，请系好安全带，飞机就要起飞。表示即将做，用现在进行时表示将来时。选B。
