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: What is a main feature of plains?  
 (A) a flat, level surface (B) a high, steep peak (C) a low, shallow basin (D) a gentle, gradual slope

Output: A


Input: Consider Input: When nitrogen-rich runoff from farms enters a nearby farm, it causes abundant growth of algal mat on the pond surface. As a result, underwater plants in the pond begin to die. Identify the limiting factor that is most responsible for causing the underwater plants to die.  
 (A) oxygen (B) sunlight (C) nitrogen (D) carbon dioxide

Output: B


Input: Consider Input: The bacteria Escherichia coli (E. coli) live in the intestines of humans and make vitamins such as vitamin K and B-complex vitamins. Which would best describe the relationship between E. coli and humans?  
 (A) The E. coli benefit and humans are harmed. (B) There is only a benefit for the humans. (C) There is only a benefit for the E. coli. (D) The E. coli and humans both benefit.


Output: D