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.

Example Input: When the cardboard cone of a radio speaker vibrates, it produces a sound in the air around it. The cone produces this sound by transferring which of the following to the air around it?  
 (A) heat (B) current (C) wave motion (D) magnetic force
Example Output: C

Example Input: Which of the following units best represents the density of an object?  
 (A) kg (B) hr (C) m/s^2 (D) g/cm^3
Example Output: D

Example Input: In which group of animals below are all of the members well adapted to living in a forest ecosystem?  
 (A) field mouse, rabbit, pheasant (B) gull, tree frog, grasshopper (C) coyote, antelope, bison (D) squirrel, deer, woodpecker
Example Output:
D