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]: When animals use energy, they produce  
 (A) nitrogen (B) iron sulfide (C) oxygen (D) carbon dioxide
[EX A]: D

[EX Q]: Which of the following is an example of a behavioral adaptation?  
 (A) hooves of a horse (B) migration of birds (C) a spider web (D) a bee hive
[EX A]: B

[EX Q]: A student hypothesizes that the amount of water a plant receives will affect how long it grows before reaching maturity. To test this hypothesis, the student will need  
 (A) several digital scales. (B) a wet paper towel. (C) several identical plant seeds. (D) different sizes of containers.
[EX A]:
C