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: What determines how long the Moon takes to complete one cycle of phases?  
 (A) the period of rotation of the Moon around its axis (B) the period of revolution of the Moon around Earth (C) the period of rotation of Earth around its axis (D) the period of revolution of Earth around the Sun

SOLUTION: B

PROBLEM: Which substance do all living things require to survive?  
 (A) blood (B) water (C) carbon dioxide (D) organic soil

SOLUTION: B

PROBLEM: A factory in Japan had been dumping mercury into Minamata Bay. Certain microorganisms in the water were able to change the mercury into a form that the plankton could use. Which most likely happened next?  
 (A) The organisms built up a resistance to the mercury. (B) The mercury passed through the food chain. (C) The plankton made the mercury safe. (D) The fish would not eat the plankton.

SOLUTION:
B