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.

Rhinoceroses and horses are related. They have very similar digestive systems and an odd number of toes on their feet. Horses have one toe, and rhinoceroses have three. These facts best support which claim?  
 (A) Horses and rhinoceroses share a common ancestor. (B) Horses and rhinoceroses are genetically identical. (C) Horses are the ancestors of modern rhinoceroses. (D) Horses have descended from modern rhinoceroses.
A

If an atom has two protons and three electrons, then the atom is  
 (A) positively charged. (B) negatively charged. (C) radioactive. (D) neutral.
B

If a nerve cell stopped functioning, the cell would  
 (A) start producing oxygen. (B) begin dividing into more cells. (C) become a different type of cell. (D) stop sending signals to the brain.

D