In the Photolytic Cleavage of Water by the Oxygen-Evolving Complex $\rightarrow$

In the photolytic cleavage of water by the oxygen-evolving complex [2H₂O $\rightarrow$ 4 H⁺ + 4e^- + O₂],how many photons of light at a wavelength of 680 nm are required?

A) 1
B) 2
C) 4
D) 6
E) 8