Which of the Following Is the BEST Explanation for an Extended

Which of the following is the BEST explanation for an extended childhood period in human development?

A) During this time, a human's immune system reaches its full potential.
B) A long childhood period is a "left over" adaptation from the time when the human life span was considerably shorter than it is today.
C) Rebellion against authority is a necessary step in the evolutionary development of independent behavior.
D) During this time, humans develop a large brain and gain experience required to master the complexities of human society.