Why Isn't Oxygen Produced by Organisms That Perform Anoxygenic Photosynthesis

Why isn't oxygen produced by organisms that perform anoxygenic photosynthesis?

A) their photosystems do not utilize the Calvin cycle
B) they use a different enzyme for the initial reactions of the Calvin cycle ​
C) they use electron donors other than water ​
D) their membranes lack ATP synthase ​
E) their chlorophyll contains an iron center rather than magnesium ​