You are given a science question (easy-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:
Which of the following is closest to the percentage of the total water on earth that is freshwater?  
 (A) 100% (B) 90% (C) 70% (D) 3%

Ex Output:
D


Ex Input:
Vehicle exhaust contains a form of pollution called particulate matter. Technologies are being developed to reduce the amount of particulate matter in exhaust. A vehicle that produces less particulate matter would have the greatest impact on which aspect of human health?  
 (A) heart health (B) respiratory health (C) the rate of birth defects (D) weight and physical fitness

Ex Output:
B


Ex Input:
Most types of cacti survive the dry conditions of a desert because they hold water in their stems. This is an example of  
 (A) a niche. (B) a species. (C) an adaptation. (D) an ecosystem.

Ex Output:

C