According to Your Authors, What Would Be the Best Response

According to your authors, what would be the best response to a 5-year-old's question "Where do babies come from?"

A) Tell the child he is too young to know at present but reassure him you will discuss this when he is older.
B) Explain the male and female reproductive systems to your child in detail, using diagrams if possible, then explain the birth process in a similar fashion.
C) Briefly discuss the basics of sexual intercourse, check to see whether your child has understood your answer, and express your openness to answer similar questions in future.
D) Tell your child it is an inappropriate question for a child to ask.