说明：  某车辆经销商经营的车辆种类有小汽车、卡车、摩托车和吉普车等，每种车辆信息主要包括车辆型号、生产商、准乘人数和车辆价格等，卡车还有载货量等信息。被销售的车辆的销售信息主要包括车辆信息、销售日期、售货员等。请根据如上描述为该经销商设计并实现一个车辆销售管理系统以实现对车辆销售信息的有效管理，具体包括车辆销售信息的添加、删除、修改、查询、统计和保存（必须保存至文件）等功能。
(A certain vehicle classes of vehicles dealers have cars, trucks, motorcycles and jeeps, etc., each vehicle information includes vehicle models, manufacturers, prospective by the number and price of vehicles, trucks are loading and other information. Vehicles were sold sales information mainly include vehicles of information, the date of sale, salespersons. As described in accordance with the dealers to design and realize a vehicle sales management system to realize vehicle sales information for the effective management, including vehicle sales information to add, delete, modify, query, statistics and preservation of (the need to preserve to the document), etc. function.)