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.

[EX Q]: Which of the following properties best describes a material's ability to resist scratching?  
 (A) weight (B) flexibility (C) length (D) hardness
[EX A]: D

[EX Q]: The energy that is stored in food originally comes from  
 (A) air (B) soil (C) sunlight (D) water
[EX A]: C

[EX Q]: When one form of energy is converted into other forms of energy, the total amount of energy  
 (A) varies throughout the conversion. (B) increases because some energy is created. (C) remains constant throughout the conversion. (D) decreases because some energy is destroyed.
[EX A]:
C