Which of the follow BEST summarizes the purpose of Section 4 of the 25th Amendment?

AIt provides a check on presidential power in times of war.
BIt provides a way for the president to retain his power, even if he is impeached.
CIt outlines the procedures to be followed in the case that the vice presidency is vacant.
DIf the president is incapable, or unfit to perform his duties, this section provides a means of removing the president from office.

Which of the follow BEST ...