问题
选择题
All passengers________are expected to fasten the seat belts when the plane takes off or lands. [ ]
A. on the board
B. on board
C. on boards
D. on a board
答案
答案：B
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All passengers________are expected to fasten the seat belts when the plane takes off or lands. [ ]
A. on the board
B. on board
C. on boards
D. on a board
答案：B