You are given a science question (hard-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: A container is filled with a mixture of sand and an unknown substance. What should a student do to determine whether iron particles are in the mixture?  
 (A) heat the mixture (B) filter the mixture (C) pour water into the mixture (D) pull a magnet through the mixture

A: D
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Q: High-pressure systems stop air from rising into the colder regions of the atmosphere where water can condense. What will most likely result if a high-pressure system remains in an area for a long period of time?  
 (A) fog (B) rain (C) drought (D) tornado

A: C
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Q: Which part of a pine tree makes food?  
 (A) root (B) cone (C) trunk (D) needle

A:
D
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