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.

Ex Input:
A student gives a red toy car a push on a wooden floor. The student then pushes the same red toy car on a cement floor. Which question is the student most likely investigating?
(A) How fast does a toy car usually roll? (B) What is the best way to make a toy car roll? (C) Which surface allows a toy car to roll farther? (D) Does color have an effect on the distance a toy car rolls?

Ex Output:
C

Ex Input:
An example of a solid turning into a liquid is
(A) steam turning into water. (B) water turning into steam. (C) ice turning into water. (D) water turning into ice.

Ex Output:
C

Ex Input:
Water in the solid phase has a crystal structure which keeps molecules farther apart than water at certain temperatures in the liquid phase. This relationship explains which property?
(A) the presence of more impurities in ice than in liquid water (B) the ability of ice to float on liquid water (C) the release of heat when liquid water turns into ice (D) the cooling of liquid water as it flows over ice

Ex Output:
B