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]: Proxima Centauri is the closest star to the Sun. Which units do astronomers most often use for the distance between Earth and Proxima Centauri?  
 (A) miles (B) meters (C) light years (D) astronomical units
[EX A]: C

[EX Q]: DNA technology has improved greatly in the last twenty years. Which task has been made easier by the development of DNA technology?  
 (A) identifying genetic disorders (B) determining the parts of an atom (C) observing distant objects in space (D) making very accurate measurements
[EX A]: A

[EX Q]: What travels through the stem of a plant?  
 (A) water and food (B) food and nectar (C) nectar and soil (D) soil and water
[EX A]:
A