second year secondary exam in Egypt

If I may answer, what about "rained" a past tense. In addition, I think "had been raining" may work.

Yet, I have a problem with the sentence itself; 

Did the people water their fields with the rain? Or Did the rain "water the fields"?

That's why I think the second part should be modified to "The farmers had their fields watered'

Any way, I'm waiting for the teachers' answer.

Hi,

Mr.Musa posted:

Hello everyone,

It ........... for 3 days.The farmers were very happy to water their fields.

A. has been raining 

B.rained

C. is raining 

D.was raining 

This sentence is from the second year secondary  exam in Egypt, and I think the four choices are wrong.

What's your opinion? With a reference,please. 

Thanks in advance!

David, our dear moderator, has actually given a detailed answer to this question here: https://thegrammarexchange.infopop.cc/topic/tenses-51

BTW, I completely agree with his answer and explanation.