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:
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:
Which question will best help a student determine the composition of an unknown substance?  
 (A) Is the sample warm or cold? (B) How valuable is the sample? (C) Has the sample ever been melted? (D) Does the sample conduct electricity?

Ex Output:
D


Ex Input:
Under which conditions would a sugar cube dissolve most quickly when placed in a liter of water at room temperature?  
 (A) A whole sugar cube is added and the water is stirred. (B) A whole sugar cube is added and the water is not stirred. (C) A crushed sugar cube is added and the water is stirred. (D) A crushed sugar cube is added and the water is not stirred.

Ex Output:

C