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: Which human organ system eliminates liquid and gaseous wastes from the body?  
 (A) circulatory (B) endocrine (C) excretory (D) reproductive

SOLUTION: C

PROBLEM: Which object is best used to demonstrate the bending of light as it passes through a substance?  
 (A) convex lens (B) flat mirror (C) opaque rod (D) concave mirror

SOLUTION: A

PROBLEM: Which of the following is a characteristic of the "steady state theory" of the universe?  
 (A) The universe is constantly growing and changing. (B) A great explosion caused the origin of the universe. (C) The nature of the universe has always been the same. (D) Light moving from the center of the universe appears red.

SOLUTION:
C