Detailed Instructions: 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.
Problem:The elements carbon, hydrogen, and oxygen are parts of many different compounds. Which explains why these three elements can make so many different compounds?  
 (A) They can be solids, liquids, or gases. (B) They come in different sizes and shapes. (C) They combine in different numbers and ratios. (D) They can be a proton, a neutron, or an electron.
Solution:
C