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:
Adaptive characteristics that help dolphins survive life in the ocean include all of these except  
 (A) their sleek skin. (B) swimming very fast. (C) their body shape. (D) traveling alone.

Ex Output:
D


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:
Certain lakes in the northeastern part of the United States have had decreases in pH levels, causing the deaths of many fish. What is the most likely reason for this change in pH levels?  
 (A) nuclear power plants (B) hydroelectric power plants (C) coal-burning factories (D) noncommercial farms

Ex Output:

C