单项选择题
A.tire；did；do B.tiring；have；done C.tired；do；do D.tired；have；been doing
You must explain（）how they succeeded（）the experiment.A....
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
We（）every day when we were children.A.used to swimB.use...
单项选择题We（）every day when we were children.
A.used to swim B.used to swimming C.use to swim D.use to swimming
We must make a difference between（）language and（）langua...
单项选择题We must make a difference between（）language and（）language.
A.spoken；written B.speaking；written C.speaking；writing D.speak；write
