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 unit of measurement describes an object's length?  
 (A) meter (B) kilogram (C) liter (D) degree
[EX A]: A

[EX Q]: A girl signals her friend by shining a flashlight on a mirror. Her friend can see the signal because  
 (A) heat energy can be transferred from one object to another (B) mechanical energy can be transferred from one object to another (C) sound energy can be reflected from one object to another (D) light energy can be reflected from one object to another
[EX A]: D

[EX Q]: What is the primary job of red blood cells?  
 (A) transport oxygen (B) remove waste (C) fight disease (D) allow reproduction
[EX A]:
A