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]: 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]: One hot summer, a grassland experienced a drought. Which most likely happened in the ecosystem during this time?  
 (A) The competition for food among primary consumers increased. (B) Nutrients cycled through the system at a faster rate. (C) Less solar radiation was able to enter the system. (D) Secondary consumers became extinct.
[EX A]: A

[EX Q]: Students combined baking soda and vinegar to demonstrate a chemical reaction. What indicates that a chemical reaction occurred?  
 (A) the formation of bubbles (B) a reduction in total mass (C) the disappearance of atoms (D) an increase in the number of atoms
[EX A]:
A