The students are studying ---------the wall A.on B.in C.at D

The students are studying _________the wall.A.on B.in C.at D.under 你这题出得很怪,没有一个较合适,on the wall在墙上,in the wall在墙里 at the wall在墙边 under the wall在墙下.实在要给答案,貌似选C吧.