When chemicals react in a closed container, which must be true? A The mass both before and after the reaction is the same.
B. The mass both before and after the reaction is variable.
C. The same number of compounds is present both before and after the
reaction.

I think its B.

Explanation:

Its b, because if we take for example, solid and liquid, two different masses, it produces different mass so it's not A. It's not c because we wouldn't know if the compounds are same or not. So, I strongly recommend you to go with B.

all fossil fuels are nonrenewable, so think coal, gasoline, things that we will eventually run out of. all fossil fuels are nonrenewable resources, but not all nonrenewable recourses are fossil fuels. these resources are not being renewed as fast as we are using them. i hope this considering there weren't any answer choices.

what events in mexico's history might explain why the country continues to have difficulty improving social justice and economic opportunities for all people?