A biologist trying to determine the mechanism of adenosine triphosphate (ATP) production in a newly discovered bacterium provides several different substrates on which the bacteria can feed. Which of the following results would indicate that the species uses fermentation to produce ATP?

a. After the bacteria break down their substrate, the biologist notices a rotten egg smell.
b. The biologist discovers that the bacteria are able to produce organic molecules by metabolizing methane.
c After exposure to amino acids, the bacteria produce a smell like rotting flesh.
d. The bacteria utilize glucose and produce carbon dioxide as a by-product of respiration