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:
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

Ex Output:
D


Ex Input:
Wolves have adapted skills for hunting large hoofed animals such as elk, deer, or moose. Wolves tend to target prey animals that are sick or weak. The wolf benefits from this strategy because it uses less energy to hunt. How would the prey animal population also benefit from this strategy?  
 (A) by promoting detrimental genes (B) by stimulating beneficial DNA mutations (C) by preventing the introduction of other predator species (D) by increasing the reproductive success of healthy prey animals

Ex Output:
D


Ex Input:
Which of the following is NOT a mixture?  
 (A) Smoke (B) Sugar (C) Milk (D) Paint

Ex Output:

B