Answer:
constant
Explanation:
The universe is an isolated system. In thermodynamics, an isolated system is a system that does not exchange neither matter (mass) nor energy with the external surroundings.
As a consequence, the energy and mass of an isolated system is always constant (because it cannot be exchanged with the outside): this is known as law of conservation of energy, and it can be applied to the universe as well, since it is an isolated system.
So, the correct answer is
The total amount of energy and mass in the universe is constant
