The twin paradox is an example of which of the following?

"The twin paradox is an example of which of the following?"

time dilation

The twin paradox is the theory that if one of two twins travels at near the speed of light for a while, then returns to Earth, then the twin who travelled is now younger than his brother. 

I agree that the answer is time dilation.  I'm posting a comment.  If that fifth choice was supposed to be "c" meaning the speed of light, then it should have been a lowershift c, not an uppershift C. 

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