选择程序自选动作optional library of program: 任先程序库; 任选程式库; 任选程序库recruitment optional program: 招聘备择方案optional fees or optional additional: 选择卸货港附加费mandatory or optional: 必选或可选的not compulsory optional: 非强迫的下载手机词典可随时随地查词查翻译