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: Which body system's primary function is the continuation of the species?  
 (A) digestive (B) nervous (C) excretory (D) reproductive

A: D
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Q: How many valence electrons does selenium have?  
 (A) 3 (B) 5 (C) 6 (D) 8

A: C
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Q: Which statement about the Sun is true?  
 (A) The Sun is a very large star that exists far from the Milky Way Galaxy. (B) The Sun is at the center of the Milky Way Galaxy. (C) The Sun is a medium-sized star near the edge of the Milky Way Galaxy. (D) The Sun has the Milky Way and several other galaxies moving in orbits around it.

A:
C
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