Answer:
A) If the domain of y=cos(x) is restricted to [0, π], y=cos^-1(x) is a function.
Explanation:
In order for the inverse function to be a function, the original must pass the horizontal line test: a horizontal line must intersect the function in only one place.
As you can see from the attached graph, restricting the cosine function to the domain [0, π] allows it to pass the horizontal line test, so its inverse will be a function.
__
Restricting the domain to [-π/2, π/2] does not limit cos(x) to something that will pass the horizontal line test.