— Has your son come back from abroad for the winter vacation?

— Yes. But he stayed at home for only a week. Now he       back to college.[ ]

A. went

B. has gone

C. was going

D. will go

解放思想、实事求是辩证统一的基础是( )。

A．社会实践
B．辩证唯物主义和历史唯物主义
C．改革开放
D．中国特色社会主义