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 Q]: Which of the following is the main role of flowers found on most flowering plants?  
 (A) to take in air (B) to produce seeds (C) to absorb nutrients (D) to protect the stem
[EX A]: B

[EX Q]: In the United States, which is responsible for ensuring the safety of the country's drinking water?  
 (A) Environmental Protection Agency (EPA) (B) Food and Drug Administration (FDA) (C) National Oceanic and Atmospheric Administration (NOAA) (D) Center for Disease Control (CDC)
[EX A]: A

[EX Q]: Which action is the best method to separate a mixture of salt and water?  
 (A) using a magnet to extract the salt (B) adding a colored dye to the mixture (C) pouring the mixture through a filter (D) boiling the mixture until the water evaporates
[EX A]:
D