The correct option is A Because of Catherine's relationship with the powerful king of Spain
Option A - Pope Clement denied an annulment mainly because Catherine's nephew, Emperor Charles V of Spain, had laid siege to Rome and essentially was holding the Pope as prisoner. Thus, the Pope wanted to use Catherine's powerful relationship with the King of Spain to get out of England out trouble.
Thus, option A is CORRECT.
Option B is INCORRECT because Catherine was not related to the King of France.
Option C is INCORRECT because Catherine was not related to the King of Germany.
Option D is INCORRECT because Catherine was not related to the King of Austria.