Which of the Following Is an Example of Intraindividual Variation

Which of the following is an example of intraindividual variation?

A) Drew and Alan are both 40-year-olds, but Drew is a high school dropout and Alan has a PhD in nuclear physics.
B) Dana's vision started to deteriorate when she turned 40, but her twin brother's vision remained at 20/20 for the next five years.
C) Brie's hair turned white when she turned 40, but she maintained muscle mass with daily visits to the gym.
D) Mickey was the only male at his 20th high school reunion who was not showing a "middle age spread."