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
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Q: Which is the best tool for measuring the temperature of lake water?  
 (A) Meter stick (B) Balance (C) Graduated cylinder (D) Thermometer

A: D
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Q: Which series correctly represents the levels of organization in an organism?  
 (A) cells -> organs -> organ system -> tissue (B) cells -> tissue -> organs -> organ system (C) tissue -> cells -> organ system -> organs (D) tissue -> organ system -> cells -> organs

A:
B
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