题目内容
Mr. Wu often spends lots of time ______ difficult problems______ us.
A.to explain; for B.explaining; for C.to explain; to D.explaining; to
练习册系列答案
相关题目
题目内容
Mr. Wu often spends lots of time ______ difficult problems______ us.
A.to explain; for B.explaining; for C.to explain; to D.explaining; to