In this task, you need to answer basic science questions. For each question, several terms are intentionally masked with ***. This masking can cover very few or many of the question words. Clearly, if masked terms are important, the modified question will be impossible to answer. Please indicate the correct answer with one of the following responses: "A", "B", "C", "D" or "E". While "A"-"D" correspond to the answer options provided in the input, "E" represents "I don't know" for questions that do not provide enough information. Respond via "E" if the question is not answerable. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D', 'E'.

[Q]: Question: What is the smallest unit of an element that still has the properties of that element?  (A) an atom (B) a compound (C) an electron (D) a molecul.
[A]: A.


[Q]: Question: What is the main source of *** *** on Earth?  (A) fire (B) volcanoes (C) the sun (D) electricit.
[A]: C.


[Q]: Question: Drew knows that *** is *** on its ***. He also knows this tilt is responsible for the *** that a region on *** will experience. When the *** *** is *** *** the ***, what *** will it be in ***?  (A) fall (B) spring (C) summer (D) winte.
[A]:
E.