Answer
The correct answer is:
(b) The sister who remained on Earth is older than her traveling twin once they are reunited on Earth.
Work Step by Step
We can assume that the sister on the space mission was traveling at a high speed. Then a clock in the inertial reference frame of the space mission moves more slowly than a clock on the Earth. Therefore, the sister on the Earth ages more quickly than the sister on the space mission.
The correct answer is:
(b) The sister who remained on Earth is older than her traveling twin once they are reunited on Earth.
