Mass is a property of the object. It doesn't depend on anything else,
and it doesn't change when the object goes to different places.
Its mass is always the same.
If it's 20,000 kilograms on Earth, then it's 20,000 kilograms on the
Moon, on Mars, in school, in bed, in love, in trouble, in water,
on Pluto, on Halley's comet, or in free fall in outer space.
That's why choice-B is the correct choice.
Now, if the question was talking about WEIGHT, then we would have
a lot to talk about, because WEIGHT depends on where you are, and
what else is around you. But mass doesn't.
