TASK DEFINITION: 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.
PROBLEM: Which unit is used to express the amount of energy in food?
(A) Calorie (B) degree Celsius (C) milliliter (D) gram

SOLUTION: A

PROBLEM: Which system of the human body provides protection to most of the major organs?
(A) skeletal system (B) circulatory system (C) respiratory system (D) muscular system

SOLUTION: A

PROBLEM: Which stimulus causes a porcupine to extend its quills?
(A) lunar effect on Earth (B) seasonal temperature changes (C) threatening behavior by predators (D) environmental encroachment by humans

SOLUTION:
C