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.

Example Input: Which form of energy are x rays and ultraviolet light?  
 (A) nuclear (B) heat (C) electromagnetic (D) chemical
Example Output: C

Example Input: Which type of organism is at the lowest level of the food chain?  
 (A) autotroph (B) heterotroph (C) carnivore (D) omnivore
Example Output: A

Example Input: When Isaac Newton theorized that gravity caused objects to fall to the ground, he had also discovered the force that causes  
 (A) chemicals to react. (B) volcanoes to erupt. (C) lightning to strike Earth. (D) the planets to orbit the Sun.
Example Output:
D