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]: The systems of the human body work together. Which system works with the skeletal system by pulling on the bones to create movement?  
 (A) digestive (B) circulatory (C) muscular (D) nervous
[EX A]: C

[EX Q]: The endangered Florida manatee is a large, aquatic mammal that feeds on sea grasses in brackish water. Due to where they like to feed, manatees are vulnerable to injuries from boat propellers. If speed zones requiring boats to maintain a low speed are placed in areas where manatees are known to congregate, which will most likely occur?  
 (A) less water pollution in manatee habitats will occur (B) manatees will seek alternate food sources (C) new manatee predators will surface (D) manatee populations will increase
[EX A]: D

[EX Q]: Lori owns a house next to the lake. She uses lots of fertilizer to keep her lawn green. Which impact could fertilizing her lawn have on the lake?  
 (A) an increase in the algae population (B) an increase in the fish population (C) an increase in the mosquito population (D) an increase in the lake's depth
[EX A]:
A