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: The human immunodeficiency virus (HIV) causes AIDS. The first known human cases AIDS were in Africa in the late 1950s. Since then, tens of millions of people have died from the disease, and tens of millions more people all over the world are infected. Which term best describes the disease AIDS?  
 (A) isolated cases (B) outbreak (C) epidemic (D) pandemic
Example Output: D

Example Input: Because copper is a metal, it is  
 (A) liquid at room temperature (B) nonreactive with other substances (C) a poor conductor of electricity (D) a good conductor of heat
Example Output: D

Example Input: When taken to a new habitat, non-native plants often threaten native plants of the new habitat. Why do non-native plants threaten native plants?  
 (A) Non-native plants are able to mutate rapidly. (B) Non-native plants cause native animals to relocate. (C) Non-native plants are able to be used for medicine. (D) Non-native plants compete with native plants for resources.
Example Output:
D