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: A population of plants growing on an island consisted of two varieties, one with thorns and the other without. Over a period of many years, the variety with thorns gradually disappeared. Which process most likely brought about this change in the plant population?  
 (A) gene flow (B) genetic drift (C) natural selection (D) random mutation

Answer: C


Question: Fertilizers added by farmers to the soil contain high amounts of nitrates. How do fertilizers affect the nitrogen cycle?  
 (A) More nitrates are available for plants to absorb. (B) More nitrates are available for animals to eat. (C) More nitrogen gas is released into the atmosphere. (D) More nitrogen is converted by bacteria into nitrates.

Answer: A


Question: All living things contain which element?  
 (A) helium. (B) sodium. (C) copper. (D) carbon.

Answer:
D