Which letter is difficult to understand?A.U B.W C.Y D.Q

Which letter is missing? Which letter is a which letter is drink? which letter is for Which letter is ‘you’? which letter is inscert? Which letter is an insect? Which letter is an insect which letter is for drink? which letter is not me? Which letter is an insect? which letter is a question? Which letter is a question? Which letter is a vegetable Which letter is a drink? Which letter is a question? Which letter is the ocean? Which letter is you?It is( ).