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.

Which force produces energy as heat?  
 (A) pull (B) gravity (C) friction (D) magnetic
C

Andre learned that plants survive through a process called photosynthesis. Which substance do plants produce during photosynthesis?  
 (A) minerals (B) nitrogen (C) soil (D) sugar
D

A helium-filled balloon is released into the atmosphere. As the balloon rises, which would most likely increase and cause the balloon to burst?  
 (A) the mass of the helium (B) the density of the helium (C) the volume of the helium (D) the temperature of the helium

C