Sara must be fed up ______ studying

The correct answer is with. The phrase 'fed up with' is a fixed English idiom that means tired, bored, or annoyed with something that has been happening for too long. In the sentence, 'Sara must be fed up ______ studying,' the correct preposition is 'with'. 'Of', 'about', and 'from' are not used with 'fed up' in this context. Therefore, 'with' is the correct answer.