During electrolytic reduction of alumina, why do the carbon anodes need to be replaced periodically?

1. At the anode, oxide ions are oxidised and oxygen gas is liberated. 2. The anodes are made of carbon (graphite). 3. The hot liberated oxygen reacts with the carbon anodes to form carbon dioxide gas. 4. The anodes are thus gradually consumed and must be changed from time to time. 5. Option about aluminium clogging the anode is wrong, as aluminium deposits at the cathode. 6. Option about cryolite dissolving the anodes is wrong, as cryolite only lowers the melting point. 7. Option about current melting the anode into the cathode is wrong, as the loss is by oxidation, not melting. _Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 8 "Metallurgy", p.113_