Question

Read the sentence.

Although rain had been predicted, the flag was still raised.

Identify the adverb clause.

was still raised

rain had been predicted

Although rain had been predicted

the flag was still raised

Answer 1

Hi and welcome to QuestionCove!
So the adverb clause would in some way modify the action in the sentence. It would also not be able to stand on its own as a complete sentence.
In this case, I think "Although rain had been predicted" best fits.