Question

It's seven o'clock in the evening.It'time()dinner.A.in B.for C.at

请说明为什么

Answer 1

为你解答。
It's seven o'clock in the evening. It's time (B.for) dinner.
现在是晚上七点。到吃晚餐的时间了。
解释：It's time for sth，到了做某事的时间。这里要用介词for表示“对于……”。

追问

为什么不能用to呢？^_^

追答

用to的时候是用的动词不定式，而不是动词。这句话应该这么表达：
It's time (to have) dinner.
也就是说to要和动词原形一起用。

Answer 2

for

it is time for(后跟名词）

it is time to do sth(跟动词的用法）

到了该做什么事情了，这个句式，没有其他的介词用法

Answer 3

It's seven o'clock in the evening.It'time(B.for )dinner.