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.

The number of fish in a lake suddenly increases. How will the increase most likely affect the lake?  
 (A) There will be less water in the lake. (B) More plants will grow in the lake. (C) More frogs will live in the lake. (D) There will be fewer insects in the lake.
D

Which involves the greatest variety of cell types?  
 (A) a tissue (B) an organ (C) an organ system (D) an organism
D

The population of which of the following 26 organisms would most likely decline if small animals like rats, rabbits, and snakes were eliminated from an ecosystem?  
 (A) earthworms (B) grasses (C) hawks (D) mushrooms

C