The enzyme nitrogenase is inhibited by oxygen. Which of the following does NOT protect nitrogenase from oxygen?

A) special thick-walled cells (heterocysts) in filamentous cyanobacteria, such as Anabaena
B) special nitrogenase-protecting proteins in Azotobacter species
C) temporal separation of nitrogen fixation (at night) and photosynthesis (during the day) in some species of cyanobacteria
D) growth under aerobic conditions
E) growth under anaerobic conditions