Answer
b
Work Step by Step
We were given that the proper time is 25 seconds, so we look at the time dilation equations.
$\Delta t=\Delta t_0 / \sqrt{1-\beta^2 }$
$\Delta t=25s / \sqrt{1-\beta^2 }$
As we can see, as $\beta$ gets larger, $\Delta t$ grows non-linearly. The only curve on the graph that grows non-linearly is "b".
