If the speed doesn't change, no work is done.
The part about starting and stopping only confuses the question. They say the speed is constant, so forget about stopping and starting processes.
An object of mass m travels halfway around a circle at a constant speed v. The magnitude of the total work done on the object by the net force acting on it (not counting starting and stopping at the beginning and end of the path) is
a. equal to mv
b. equal to 2mv
c equal to mv^2
d. equal to 0
e. equal to 1/2mv^2
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