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.

Input: Consider Input: To calculate the relative age of rocks, geologists use the rate of radioactive decay of isotopes present in their samples. What is the term used for the original amount of the elemental isotopes being investigated?   
 (A) rare earth isotopes (B) son isotopes (C) daughter isotopes (D) parent isotopes

Output: D


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

Output: C


Input: Consider Input: A student is collecting water samples. The student needs a container that holds water, will not break easily, and can be used many times. Which of the following containers will best meet the student's needs?  
 (A) a glass jar (B) a paper cup (C) a wooden box (D) a plastic bottle


Output: D