Here, both sentences are independent, which means that the correct answer is B whichever sentence is underlined.
Independent clauses are complete on their own and do not need to be located within larger sentences because they are those larger sentences, which is the case here. On the other hand, subordinate clauses cannot stand on their own because they feel incomplete - thus, they have to be located within a larger sentence, which is not the case here as there are no subordinate clauses.
