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: Researchers are developing new types of crop plants with desirable characteristics such as disease resistance and drought tolerance. Crossing plants so that the next generation will express desirable traits is best described as  
 (A) selective breeding. (B) natural selection. (C) genetic engineering. (D) gene sequencing.

Answer: A


Question: What property is the same for each atom of an element?  
 (A) energy (B) mass number (C) atomic number (D) number of neutrons

Answer: C


Question: What is the primary source of energy for organisms from a beach ecosystem?  
 (A) sand (B) oxygen (C) the Sun (D) the ocean

Answer:
C