It will be a. <span>benzene.</span>
Do you mean; " A blank is a substance that is made by combining two elements?" (I'm not sure if substances is the right term)
If so then the blank is a compound.
Answer:
(a): 2ZnO(s) -----------> 2Zn(s) + O2(g)
2C(s) + O2(g) ---------> 2CO(g)
(b): ZnO(s) + C(s) ---------> Zn(s) + CO(g)
All of the above I think it might not be right
The balanced equation is:

Then proceed with the following equations.

The answer is

.