题目内容：

（ ）Mary and her classmates that helped the old man clean his house
A.it were B.they were C.it was D.there were

优质解答

选C
句型：it is s.b /s.th that.
此类句型不管it 后面跟的是单数或是复数,均视作一个单的物品,所以用单数,判断选C