Answer:
"changes the period to pi"
Explanation:
f(t) = Sin(t),
Here, t is the period, by definition.
Multiply t by a number that is GREATER THAN 1, makes the period shorter and compressed.
Multiplying t by a number that is between 0 and 1 makes the period expanded.
For the first, if we multiply the period by a, the period becomes

Since the problem tells us to multiply by 2, we know the period becomes compressed and becomes :

Third answer choice is right.