从1951年起，我国采用怎样的易货方式？（）
A.公私兼顾
B.摆脱禁运
C.先进后出
D.货物等价
参考答案：C
The sun is _____________ the moon. [ ]
A. much bigger than
B. a lot more bigger than
C. much more bigger as
D. a lot more big as
简述LF中Ar气的主要作用。
