Definition: You are given a science question (hard-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.
Input: A mountain with a melting glacier has a stream with a waterfall. The waterfall fills a lake at the base of the mountain. Where is the water coldest?
(A) glacier (B) stream (C) waterfall (D) lake
Output:
A