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).

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

[EX Q]: Question: The Grand Canyon is a perfect example of ___, over millions of years, caused by the flow of the Colorado River.  (A) dissolving (B) deposition (C) weathering (D) erosio?
[EX A]: D.

[EX Q]: Question: Which of the following is NOT true in any particular environment?  (A) Some kinds of plants and animals survive well. (B) Some kinds of plants and animals do not survive well. (C) Some kinds of plants and animals cannot survive. (D) Some plants and animals will always survive?
[EX A]:
D.