The book mainly tells that different countries have different customs.A. graduallyB. mostl

问题补充：

The book mainly tells that different countries have different customs.

A. gradually

B. mostly

C. fully

D. normally

答案：

A. gradually

(答案→)B. mostly

C. fully

D. normally

解析：句意:这本书主语告诉了我们不同的国家有不同的风俗。mainly 的意思是主要地。gradually 渐渐的；mostly 主要地；fully 满地；normally 正常地。根据句意，故选B。