The answer is "lipids"
I think this is
These fuels are nonrenewable because they are limited substances which cannot be produced at the same rate at which it is used. Also, they cannot be REused, hence the wording non-REnewable. Hope this answers your question.
The mass of the box increased and the acceleration of the box decreased
Not entire sure because I haven't taken human anatomy but I'd guess it would have to be the digestive enzymes breaking it down