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 adaptation helps a bird fly?  
 (A) larger feet (B) bigger eyes (C) longer beaks (D) hollow bones
[EX A]: D

[EX Q]: What is the function of the nucleus in a cell?  
 (A) provides energy (B) provides nutrients (C) controls activity (D) controls movement
[EX A]: C

[EX Q]: Blood absorbs oxygen in the  
 (A) heart. (B) lungs. (C) stomach. (D) muscles.
[EX A]:
B