单项选择题
You must explain（）how they succeeded（）the experiment.
A.of us；for B.at us；at C.to us；in D.for us；to
单项选择题 We（）every day when we were children.
单项选择题 We must make a difference between（）language and（）language.
单项选择题 What a fool I have been! Why（）I think of that before?
