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.

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
B

Which substance do all living things require to survive?  
 (A) blood (B) water (C) carbon dioxide (D) organic soil
B

The BEST way to tell the DIFFERENCE between an oak and a maple tree is to compare the  
 (A) height of both trees. (B) number of leaves on the trees. (C) size of the root systems of the trees. (D) shape of the leaves.

D