Which of the Following Is an Example of Time Dilation

Multiple Choice

Which of the following is an example of time dilation?

A) As material approaches a black hole event horizon, it appears redder and redder.
B) The time that a star spends as a giant is much shorter than its main-sequence lifetime.
C) Pulsars' pulsation periods slow down as they age.
D) As a star approaches a black hole's event horizon, it appears to move more and more slowly.