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.
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Question: Proxima Centauri is the closest star to the Sun. Which units do astronomers most often use for the distance between Earth and Proxima Centauri?  
 (A) miles (B) meters (C) light years (D) astronomical units

Answer: C


Question: Planting certain crop plants in a field causes a disruption of the natural nitrogen cycle in that field. Which outcome would this disruption most DIRECTLY cause in the field over time?  
 (A) topsoil erodes (B) soil nutrients decrease (C) desert conditions appear (D) atmospheric carbon dioxide increases

Answer: B


Question: Jake's cats eat food from a can. The cats come running into the kitchen when they hear the electric can opener. Now, each time Jake's mother opens a can of corn, the cats come running. This is an example of  
 (A) learned behavior (B) correct behavior (C) instinct (D) migration

Answer:
A