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.

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
D

A population of plants growing on an island consisted of two varieties, one with thorns and the other without. Over a period of many years, the variety with thorns gradually disappeared. Which process most likely brought about this change in the plant population?  
 (A) gene flow (B) genetic drift (C) natural selection (D) random mutation
C

A girl with long hair is going to be participating in an experiment that uses an alcohol burner for an energy source. What is the best thing for her to do to prepare for this experiment?  
 (A) leave her large jacket in her locker for the day (B) use goggles during the experiment (C) tie her hair back away from her face (D) wear a lab apron during the experiment

C