If you work hard now,it is ____ you'll have a bright future.

问题描述:

If you work hard now,it is ____ you'll have a bright future.
A.sure B.surely
C.certain D.certainly
答案上说是选C,但是为什么啊?
我高一而且英语比较渣渣,所以别说深奥的,最好能够通俗易懂.
实在没法让我懂,那就算了……

B D是副词,is是系动词,系动词后面不能跟副词的;
A,是一定,太绝对了,所以选C