Girl: You're right. Boy: What 5 ______ taking notes when you revise

Explanation:

The boy is asking a question about a method of studying. The previous turn established that the girl needs advice on preparing for an exam. The phrase 'taking notes when you revise' suggests a study technique. The question 'What 5 ______ taking notes when you revise' needs a verb that forms a question about the effectiveness or suitability of this method. 'About' is the correct preposition to form the question 'What about taking notes...', inquiring about this specific strategy.

Answer:

Boy: What 5 about taking notes when you revise?