【题目】All passengers ________ are expected to fasten the seat belts when the plane takes off and lands.
A. on board B. on aboard
C. on the board D. on boards
在线课程【答案】A
【解析】
考查介词短语。A. on board在船（车或飞机）上；C. on the board在董事会上；在木板上。B、D短语错误。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。故选A。