Why Are Organisms That Presently Use Hydrogen Sulfide as an Electron

Multiple Choice

Why are organisms that presently use hydrogen sulfide as an electron source limited in their distribution and importance?

A) It is more efficient.
B) They are smaller.
C) Hydrogen sulfide is abundant and widespread.
D) Hydrogen sulfide is neither abundant nor widespread.
E) In the current environment, hydrogen sulfide combines with silicon dioxide, inactivating it.