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: 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: During a biochemical reaction, pyruvate (C3H4O3) is converted into carbon dioxide (CO2) and water (H2O). In what cellular organelle does this biochemical reaction occur?  
 (A) nucleus (B) cytoplasm (C) mitochondria (D) endoplasmic reticulum

Answer: C


Question: Louis was investigating physical and chemical changes in matter. Which of these changes that Louis found involves a chemical change in matter?  
 (A) evaporation of water (B) grinding of rock (C) melting of ice (D) rusting of iron

Answer:
D