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.

Example Input: Plants growing in a pond release a gas that fish need to survive. Which gas do the plants release that fish use?  
 (A) helium (B) hydrogen (C) nitrogen (D) oxygen
Example Output: D

Example Input: The shape of a riverbed changes over time as a result of which gradual process?  
 (A) erosion (B) dissolving (C) plate shifting (D) compaction
Example Output: A

Example Input: Maryland has many renewable and nonrenewable natural resources. Which group contains only renewable resources found in Maryland?  
 (A) wind, oil, coal (B) fish, coal, wind (C) oil, water, trees (D) trees, water, fish
Example Output:
D