All passengers are expected to fasten the seat belts when the plane takes off and lands．A

问题补充：

All passengers are expected to fasten the seat belts when the plane takes off and lands．

A. on aboard

B. on board

C. on the board

D. on boards

答案：

A. on aboard

(答案→)B. on board

C. on the board

D. on boards

解析：考查短语搭配。句中on board为“在飞机上”之意。句意：当飞机起飞和降落的时候，所有的乘客都要求系上安全带。