You are given a science question (hard-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.

Example Input: Giselle makes a model, using foam balls, to represent the events in a solar eclipse. To demonstrate this phenomenon best, the foam ball model should have which characteristic?  
 (A) the ability to revolve around the central ball (B) a magnet in each ball (C) a representation of oceans on each ball (D) a source of thermal energy
Example Output: A

Example Input: Many endangered animals are captured, tagged, and then released back into their environment. The tag may be a piece of coded plastic or metal that is placed somewhere safe on the body. Which is the most likely reason to tag an animal?  
 (A) to monitor their eating habits (B) to monitor their roaming habits (C) to monitor their sleeping habits (D) to monitor their reproductive habits
Example Output: B

Example Input: A squirrel dropped an acorn from a branch of an oak tree. Which of these will change as the acorn falls from the tree to the ground?  
 (A) the mass of the acorn (B) the force on the acorn (C) the density of the acorn (D) the velocity of the acorn
Example Output:
D