If the pattern continues for an amount of time the verb would be in present tense. The present tense verb in these options is stays which would be the answer.
We could also use elimination method.
It’s not A or C because that would mean that it had already happened and based on the given context we don’t know that it already had happened.
It also isn’t b because using a verb ending with -ing wouldn’t make sense in this sentence when you read it aloud.
