This question examines the correct usage of the verb 'differ'. The correct answer is A. 'differ in' is the correct preposition to use when indicating a difference between two subjects in a particular aspect. Option B is incorrect because 'differ from each other' is redundant. Option C is incorrect because 'differ with' is not a proper collocation. Option D is incorrect because 'differ about' is not the correct usage for indicating a difference in opinion or taste. The key point is the correct collocation with the verb 'differ'.