If an object is moving with a constant velocity, then by definition it has zero acceleration. So there is no net force acting on the object. The total work done on the object is thus 0 (that's not to say that there isn't work done by individual forces on the object, but the sum is 0 ).
The earth is considered an Open system which is B.
This is an example of Uniform Speed
EXPLANATION
Uniform Speed => no change in speed
Uniform Accelerations Speed => There is a change in speed, but the acceleration remains the same.
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