题目内容：

When the teacher entered the classroom,he found the students already ___.
A.seating
B.seated
C.sit
D.sits.

优质解答

B.seated是过去分词“让某人就坐”做宾补,这个动作是宾语的students发出的,他们自身又承受了这个动作.
seating是现在分词,表主动意义；sit和sits是谓语动词形式,不可在此做宾补；