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: Consider Input: Which example best shows structures that make up the digestive system in the human body?
(A) heart, blood, vessels (B) nose, trachea, lungs (C) brain, spinal cord, nerves (D) esophagus, stomach, intestines

Output: D

Input: Consider Input: As the molecules of water begin to slow down they go into a phase where they are no longer able to easily move past each other. The water is passing through a phase change and will
(A) remain a mixture. (B) remain a compound. (C) become an element. (D) become a compound.

Output: B

Input: Consider Input: One example of a living thing is
(A) air (B) water (C) a rock (D) a worm
Output: D