The Figure Below Shows Anaerobic Corrosion of a Piece of Steel

The figure below shows anaerobic corrosion of a piece of steel accelerated by the action of anaerobic microorganisms. What should be on label 2?
a. Elemental sulfur and iron directly react to produce $\mathrm{FeS}$ .
b. Iron reduces $\mathrm{H}_{2} \mathrm{~S}: 4 \mathrm{Fe}+\mathrm{SO}+4 \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{FeS}+3 \mathrm{Fe}^{2+}+8 \mathrm{OH}$
c. Acid rain is produced: $\mathrm{H}_{2} \mathrm{O}+1 / 2 \mathrm{O}_{2}+2 \mathrm{NO}_{2} \rightarrow 2 \mathrm{HNO}_{3}$
d. Acid rain is produced: $2 \mathrm{H}_{2} \mathrm{O}+3 \mathrm{O}_{2}+4 \mathrm{NO} \rightarrow 4 \mathrm{HNO}_{3}$
e. Acid rain is produced: $2 \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}+2 \mathrm{SO}_{2} \rightarrow 2 \mathrm{H}_{2} \mathrm{SO}_{4}$