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。