They went into the room and saw a large piano standing the wall covered with thick cloth.A

问题补充：

They went into the room and saw a large piano standing the wall,covered with thick cloth.

A. against

B. onto

C. behind

D. on

答案：

(答案→)A. against

B. onto

C. behind

D. on

解析：考查介词：句意：他们进入房间看见一个大钢琴靠在墙上，上面盖着厚厚的布。选A。