optionalityn.可选择性optionaladj.任选的Optional Application Tapes可选择的应用磁带optional altruistic suicide非强制利他性自杀optional course of humanity人文选修课optional network facilities选择网络设施optional library of program任选程序库optional transfer condition任选传送条件optional-halt instruction选择停机指令optional priority interrupt任意优先级中断Optional fight of procedure刑事程序选择权optional design requirement非强制性设计规定

1. You pay the duty at the desk and get the receipt.
   你可以在出纳台交税，然后拿到收据。
2. The government imposes a special duty on oil.
   政府征特殊石油税。