Answer:
C. Conservation
Explanation:
Mass is defined as "the amount of matter held within a body and hence stays the same, irrespective of our location, since the amount of matter will stay fixed"
The mass is a property that never change no matter the place, ambiental conditions, temperature and other possible factors.
The only possibility in order to change the mass is with chemical reactions or desintegration processes but that's very improbable. So for this reason this is an example of conservation.