It rained / was raining for eight hours. (The past simple / The past continuous)

[Tarheel]

Bob: I don't understand these instructions. Would you help me?
Rob: Sure!

Bob: I can't understand these instructions. Would you put this thing together for me?
Rob: Let me see the instructions. Oh, they're in French. Can you read French?
Bob: No.
Rob: Well, no wonder you can't understand them.

 

[bigC]

1. Both are possible.
2. Both are wrong. The past simple doesn't work because "They built" is a single finished action. It can't last for five years. The other choice is wrong because "They was building" is incorrect. "They were building ..." is possible.
3. Both are possible.

Can "built" be used to refer to the comple building activity, i.e. from the first day the activity started up to day the activity finished.

 

[emsr2d2]

Can "built" be used to refer to the comple building activity, i.e. from the first day the activity started up to day the activity finished.

Yes, but not with a timeframe, as we've repeatedly said.

I built my own house. (I was the person doing the construction work from the first day of activity to the day it was finished.)
I built my own house. It took me five years. (I was the person doing the construction work from the first day of activity to the day it was finished. The house was finished five years after I started.)
I built my own house for five years.

 

[Tarheel]

Can "built" be used to refer to the complete building activity, i.e. from the first day the activity started up to day the activity finished?

I built it. - It's finished.
I'm building it. - It's a work in progress.