不是必要的,可有可無的
Dispensable \Dis*pen"sa*ble\, a. [LL. dispensabilis. See {Dispense}.] 1. Capable of being dispensed or administered. 2. Capable of being dispensed with. --Coleridge.
dispensable adj : capable of being dispensed with or done without; "dispensable items of personal property" [ant: {indispensable}]