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: To which group does an animal belong if it lays eggs and has scales and gills?  
 (A) amphibian (B) bird (C) fish (D) reptile

SOLUTION: C

PROBLEM: Which material best conducts heat and electricity?  
 (A) metal (B) plastic (C) rubber (D) wood

SOLUTION: A

PROBLEM: A researcher is measuring changes in the density of the upper atmosphere over time. Which units should be used for the density measurements?  
 (A) kg/s (B) m^3/s (C) L/m^3 (D) kg/m^3

SOLUTION:
D