optional fee

基本解释

Optional Admission Fee are mandatory for all Passengers.
自费门票所有团员必须支付。
An optional chargeable (fee-based) function that allows you to create, import, and deploy virtual appliances in your environment.
可选的付费功能，允许在环境中创建、导入和部署虚拟设备。
Airline begins to provide optional service paying fee for the passenger before in 3 years many, included baggage to consign this service among them.
航空公司在三年多以前就开始为旅客提供可选的付费服务，其中就包括了行李托运这项服务。

Nina also includes a range of existing Nuance text-to-speech voices, and Nuance can develop a custom TTS voice for an optional development fee.
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Instead, Southwest added an optional early bird fee which allows travelers to check in earlier to get a better place in line.
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Part D is an optional insurance program that charges a monthly fee in exchange for prescription drug coverage.
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