instruction:
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.
question:
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.
answer:
D


question:
Which statement best describes how birth and death rates compare in a population at carrying capacity?  
 (A) The birth rate is greater than the death rate. (B) The birth rate is less than the death rate. (C) The birth rate is equal to the death rate. (D) The birth rate and the death rate are zero.
answer:
C


question:
Most of the concentration of which gas results from the activity of producer organisms?  
 (A) nitrogen (B) oxygen (C) water vapor (D) carbon dioxide
answer:

B