TASK DEFINITION: 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: A student is mixing a cup of hot chocolate with a spoon. How is the heat transferred between the hot chocolate and the part of the spoon that is in the hot chocolate?  
 (A) Conduction transfers energy from the spoon to the hot chocolate. (B) Conduction transfers energy from the hot chocolate to the spoon. (C) Convection transfers energy from the spoon to the hot chocolate. (D) Convection transfers energy from the hot chocolate to the spoon.

SOLUTION: B

PROBLEM: Which element makes up most of the air we breathe.  
 (A) carbon (B) nitrogen (C) oxygen (D) argon

SOLUTION: B

PROBLEM: Which of these chemical equations demonstrates the law of conservation of mass as it applies to the combustion of ethane?  
 (A) C_{2}H_{6} + 3O_{2} -> 2CO_{2} + 3H_{2}O (B) C_{2}H_{6} + 5O_{2} -> 2CO_{2} + 3H_{2}O (C) 2C_{2}H_{6} + 5O_{2} -> 4CO_{2} + 4H_{2}O (D) 2C_{2}H_{6} + 7O_{2} -> 4CO_{2} + 6H_{2}O

SOLUTION:
D