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 Input:
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 Output:
B


Ex Input:
Cell membranes allow some molecules to move freely across the membrane, while other molecules are restricted. Which term best describes this capability of a cell membrane?  
 (A) semipermeable (B) impervious (C) resilient (D) unyielding

Ex Output:
A


Ex Input:
When too much salt is detected in the bloodstream, the brain secretes a hormone that helps the body retain water by reducing the amount of urine produced. This is an example of  
 (A) a feedback loop. (B) an acquired trait. (C) a balanced ecosystem. (D) a symbiotic relationship.

Ex Output:

A