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.

Ex Input:
Which explains how the epithelium offers protection to land-dwelling vertebrates?  
 (A) Epithelium provides a rigid shell to prevent punctures. (B) Epithelium has capillaries to resist iron deficiency. (C) Epithelium insulates the vertebrate from hypothermia. (D) Epithelium prevents dehydration in vertebrates.

Ex Output:
D


Ex Input:
The prairie grass ecosystem once had a deep layer of topsoil which was protected by the grasses that covered it. Removal of these grasses for farmland is causing the soil to be eroded mainly by  
 (A) wind and rain. (B) animal movement. (C) crops grown in the soil. (D) increased temperatures.

Ex Output:
A


Ex Input:
All living things need energy to survive. What is the primary source of energy for all living things?  
 (A) plants (B) the sun (C) water (D) the wind

Ex Output:

B