In Engelmann's Classic Experiment, Why Were the Oxygen-Requiring Bacteria Clustered

Multiple Choice

In Engelmann's classic experiment, why were the oxygen-requiring bacteria clustered around the regions of Spirogyra algae that were bathed in red, blue, and violet light?

A) because photosynthesis is most active in those wavelengths of light and thus more oxygen is consumed by the algae in those regions
B) because chlorophyll is green and thus reflects green light
C) because photosynthesis is most active in those wavelengths of light and thus more oxygen is produced by the algae in those regions
D) because the bacteria were immobile and that is where Engelmann happened to place them