So, we have two reduced cytochrome C molecules give off a total of two electrons. So one electron per cytochrome C molecule. One of the electron stops at the copper B group, reducing it, as discussed here, and the other basically stops at the heme A three, reducing that heme A three. And once these two groups are in their reduced form, only then can they actually bind oxygen. So in the next step, in diagram two, we have an oxygen, and the oxygen is the same oxygen molecule that we essentially breathe in from the environment. The oxygen is basically used to form something called a peroxide bridge between this heme A three and this copper B.