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]: What is the primary function of white blood cells in humans?  
 (A) carry oxygen (B) fight disease (C) grow tissues (D) remove waste
[EX A]: B

[EX Q]: A condition in bees called "colony collapse disorder" occurs when worker bees leave the hive to collect nectar and never return. How would a decline in the bee population most likely affect a farm ecosystem?  
 (A) There would be a decrease in soil thickness. (B) There would be a decline in fruit production. (C) There would be an increase in plant diseases. (D) There would be an increase in insect pest populations.
[EX A]: B

[EX Q]: On a small, isolated island, a hurricane destroyed all the trees that produced a large, hard-shelled nut. Which bird population would most likely decrease?  
 (A) birds with long, probing beaks (B) birds with thick, strong beaks (C) birds with thin, short beaks (D) birds with large, pouch beaks
[EX A]:
B