Heat is an exchange of internal energy from one system to another due to OA. the systems having the same temperature.
ОВ.
one system being gas and the other being solid.
OC.
one system being liquid and the other being solid.
OD.
a temperature difference between the systems.

Mass is the amount of matter in an object.  weight is the measurement of the pull of gravity on an object.  say for example, you travel to the moon which has a different gravitational field compared to the gravitational field of earth. (gravitational fields: earth = 1, moon = 0.165)  now when you are on the moon, the pull of gravity on you is different than on the earth. and as weight is the measurement of the pull of gravity on an object, that means yes, your weight can and will change on the moon.  however, on the moon, on earth or even on jupiter, the amount of mass inside of you remains the same. meaning your physical mass remains constant.  in conclusion it is possible for your weight to change as your mass remains constant. 

The answer is a, because fossil fuels are burned to make energy, hence the geo (thermal) name.hope this !

Idk. but i think it is. u, oh yea idfk