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: A scientist combines oxygen and hydrogen to form water. This combination illustrates that water is  
 (A) an atom. (B) an element. (C) a mixture. (D) a compound.

SOLUTION: D

PROBLEM: In which case does a physical change occur?  
 (A) Ice melts into water. (B) Bread burns in a toaster. (C) A cake bakes in an oven. (D) Two chemicals form a new substance.

SOLUTION: A

PROBLEM: 7. What is the cause of most earthquakes?  
 (A) the rotation of Earth (B) the direction of the wind (C) the pull of Earth's gravity (D) the movement of plates on Earth's crust

SOLUTION:
D