A cat, ______ it is a white one ______ a black one, is considered to be a good cat as long as it can catch mice.

A．both; and

B．not only; but also

C．either; or

D．whether; or

关于报关企业注册登记许可与报关单位注册登记的关系；报关企业必须先向海关申请办理注册登记许可手续，然后再向海关申请办理报关单位注册登记手续；而已具有对外贸易经营权的进出口货物收发货人，可直接向海关申请办理注册登记许可手续。