Bioreactors Are Widely Used for Industrial Fermentation $\mathrm { pH }$

Bioreactors are widely used for industrial fermentation. Which of the following conditions must be closely monitored for optimal fermentation?

A) oxygen levels
B) temperature
C) $\mathrm { pH }$
D) both temperature and $\mathrm { pH }$
E) temperature, $\mathrm { pH }$ , and oxygen levels