instruction:
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.
question:
What is the primary function of white blood cells in humans?  
 (A) carry oxygen (B) fight disease (C) grow tissues (D) remove waste
answer:
B


question:
Which of the following units best represents the density of an object?  
 (A) kg (B) hr (C) m/s^2 (D) g/cm^3
answer:
D


question:
The symptoms of strep throat infection are a red and swollen throat. What is the most likely cause of strep throat?  
 (A) eating raw vegetables (B) drinking lemonade (C) invading bacteria (D) running in cold weather
answer:

C