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 Q]: Which of these senses lets Dora know when a skunk has been close to her house?  
 (A) Taste (B) Touch (C) Smell (D) Hearing
[EX A]: C

[EX Q]: Compost piles have many parts, such as leaves, moisture, vegetables, and microorganisms. Which part of a compost pile breaks down materials and adds nutrients to the soil?  
 (A) leaves (B) moisture (C) vegetables (D) microorganisms
[EX A]: D

[EX Q]: Gregor Mendel contributed to the study of biology by the careful, objective study of  
 (A) heredity. (B) bacteria. (C) pedigrees. (D) environment.
[EX A]:
A