source of additional revenue 基本例句 额外收入来源 The spokesman Stephen McNamara said the airline had considered the fee as a possible source of extra revenue since passengers had the option of not using the toilet on board.发言人纳马拉表示，既然乘客有不使用机上厕所的选择，瑞恩航空已考虑这一可能的额外收入来源。