Definition: 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: Nitrogen, a nutrient found in fertilizer, helps plants increase in size. Rainwater runoff often carries fertilizer into ponds and lakes. What effect does excess nitrogen have on organisms in a pond or lake ecosystem?
(A) Algae grows rapidly. (B) Mutations occur gradually in fish. (C) Clam shells are slowly weakened. (D) Frogs adapt quickly to new food sources.
Output:
A