Question

use the correct form of the verb given in the bracket: It..........(rain) heavily for a week and the dam was flooded.​

Answer 1

it rained heavily for a week and the dam was flooded

Answer 2

The answer to this question is rained.

It rained heavily for a week and the dam was flooded.​

When it comes to verb, it is one of the most important parts of speeches used for conveying the subject in action or describing the motion.  

They are essential parts of sentence because without verb any sentence never exists.

The past form of verb is used in the given sentence.