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.

Q: Which statement best describes the development of a human embryo?  
 (A) A single cell becomes many cells. (B) Each cell has a different function. (C) Many cells combine to form one cell. (D) All the cells have the same function.

A: A
****
Q: Which body systems are most involved in the response when someone stubs his or her toe?  
 (A) nervous and muscle (B) muscle and endocrine (C) nervous and digestive (D) reproductive and circulatory

A: A
****
Q: Which best explains why it is important for a doctor's office to keep accurate records of the medicines prescribed for their patients?  
 (A) to know how many people take medicines (B) to keep track of all of the people who are sick (C) to keep track of the next scheduled appointments (D) to know if there is a risk for harmful side effects

A:
D
****