True
Variables is changing. It is any factor, trait or condition that can exist in differing amounts or types. An experiment has three types: Independent, Dependent and Controlled.
No. We aren't the same age as the universe.
The answer is either
b A system in which Newton's Laws are valid
or
c A system in which there are no external forces.
Explanation:
not a, and not d
There are energy changes in a closed system.
A closed system obeys the conservation laws in its physical description.