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: You wish to closely observe a small insect. Which tool is the best to use?  
 (A) a balance (B) a test tube (C) a telescope (D) a magnifying glass

A: D
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Q: Which property of air does a barometer measure?  
 (A) speed (B) pressure (C) humidity (D) temperature

A: B
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Q: Scientists study the reaction of some bacteria to antibiotics, hoping to learn about a new strain of resistant bacteria. This method of gaining scientific knowledge is best described as  
 (A) observing changes in a single trial. (B) testing for a desired trait. (C) repeating steps in a procedure. (D) controlling changes in conditions.

A:
B
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