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]: When a hammer strikes a nail, the nail  
 (A) exerts balanced forces that helps it from moving. (B) exerts a force equal to the weight of the hammer. (C) exerts an unbalanced force that changes its velocity. (D) exerts an equal and opposite force back on the hammer.
[EX A]: D

[EX Q]: The cheetah population around the world has decreased because of poaching and loss of habitat. The surviving population is found to have similar alleles. Which factor is endangering the species' survival the most?  
 (A) harmful genetic mutations (B) shrinking of the gene pool (C) decrease in competition (D) increase in adaptations
[EX A]: B

[EX Q]: A ball on a cart is moving at a rate of 2 m/s. The cart suddenly stops and the ball continues to travel in the same direction at the same speed. This is an example of the  
 (A) law of gravity. (B) first law of motion. (C) second law of motion. (D) third law of motion.
[EX A]:
B