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.

[Q]: What is the primary function of white blood cells in humans?  
 (A) carry oxygen (B) fight disease (C) grow tissues (D) remove waste
[A]: B


[Q]: Which of these cycles takes 24 hours?  
 (A) Earth rotating on its axis (B) Earth revolving around the Sun (C) the Moon rotating on its axis (D) the Moon revolving around Earth
[A]: A


[Q]: Which phase change in the atmosphere forms clouds?  
 (A) evaporation (B) freezing (C) condensation (D) melting
[A]:
C