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.

Example Input: If an atom has two protons and three electrons, then the atom is  
 (A) positively charged. (B) negatively charged. (C) radioactive. (D) neutral.
Example Output: B

Example Input: A wetland habitat can continue to support the birds and fish that live there if people ___.  
 (A) drain the water away (B) flood the highest parts of the land (C) leave the land alone (D) use the land for planting crops
Example Output: C

Example Input: Which of these best defines communicable diseases?  
 (A) They can be cured. (B) They are caused by bacteria. (C) They are spread to others. (D) They can spread only in winter.
Example Output:
C