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: 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: Often organisms seem similar in their outward appearances. For example, a porpoise and a shark seem closely related, but they are not. Such similarity is the result of  
 (A) convergent evolution. (B) adaptive radiation. (C) artificial selection. (D) genetic equilibrium.
Example Output: A

Example Input: What is the smallest structural and functional unit of the nervous system?  
 (A) brain (B) organ (C) neuron (D) spinal cord
Example Output:
C