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.
--------
Question: One of the main causes of acid rain is  
 (A) Waste from nuclear power plants (B) Spills from chemical manufacturing plants (C) Gases from burning fossil fuels (D) Gases from aerosol spray cans

Answer: C


Question: Which of the following units best represents the density of an object?  
 (A) kg (B) hr (C) m/s^2 (D) g/cm^3

Answer: D


Question: When someone plays the flute, sound is produced because the air in the flute is  
 (A) hot. (B) neutral. (C) vibrating. (D) vaporizing.

Answer:
C