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: What happens at the boiling point of a substance?  
 (A) liquid becomes a gas (B) solid becomes a gas (C) liquid becomes a solid (D) solid becomes a liquid

Answer: A


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: At the end of the mitotic cell cycle, a cell divides into two cells. What must happen before the cell divides?  
 (A) The number of organelles doubles. (B) Chromosomes must be copied. (C) Four nuclei must be formed. (D) The membrane thickens.

Answer:
B