Complex IV refers to cytochrome c oxidase complex containing cytochromes.

The correct option is D a and $a_3$ and two copper centres
The enzyme cytochrome c oxidase or Complex IV is a large transmembrane protein complex found in bacteria, archaea, and in eukaryotes in their mitochondria. It is the last enzyme in the respiratory electron transport chain of cells located in the membrane. It receives an electron from each of four cytochrome c molecules, and transfers them to one dioxygen molecule, converting the molecular oxygen to two molecules of water. In this process it binds four protons from the inner aqueous phase to make two water molecules, and translocates another four protons across the membrane, increasing the transmembrane difference of proton electrochemical potential which the ATP synthase then uses to synthesize ATP. The complex contains two hemes, a cytochrome a and cytochrome a3, and two copper centers, the CuA and CuB centers. The cytochrome a3 and CuB form a binuclear center that is the site of oxygen reduction.

So the correct option is 'a and a${}_3$ and two copper centres'.