In this subtask, you will answer a simple science question. Please indicate the correct answer. If you're not sure about the answer, choose the last option "I don't know". Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D', 'E'. The "A"-"D" responses correspond to the answer options mentioned in the input. There is a 5th option "E" which should be used for questions for which you're not sure about the answer (e.g., when the questions do not provide enough information to answer).

Question: What causes nighttime and daytime on Earth?  (A) the Sun rotating on its axis (B) Earth rotating on its axis (C) Earth revolving around the Sun (D) the Moon revolving around Eart?
B
The correct answer is "Earth rotating on its axis", which corresponds to option B, because it takes about 24 hours for the Earth to make one full rotation on its axis, which is what causes the cycle of nighttime and daytime..