If your preferred trading account type is not listed, please select any available trading account type for now.
Then, in the "Additional notes" section at the bottom of the application, clearly state the specific account type and the server you wish to open.

If you wish to open a (Cent/USC) account, we currently do not support opening (Cent/USC) accounts on MT4. Please switch to MT5 first to check if the cent account option is available (account types are marked with a "Cent" icon).