使用VC6打开考生文件夹下的工程test17_1，此工程包含一个源程序文件test17_1.cpp，但该程序运行有问题，请改正程序中的错误，使程序的输出结果如下： Vehicle message Car message Vehicle message 源程序文件test17_1.cpp 清单如下: #include ＜iostream.h＞ class vehicle { int wheels; float weight; public: /***************** found *****************/ void message(void){ cout＜＜"Vehicle message\n";} }; class car:public vehicle { int passenger_load; public: /***************** found *****************/ void message (void){cout＞＞"Car message\n";} }; class truck:public vehicle { int passenger_load; float payload; public: int passengers(void){return passenger_load;} }; void main() { vehicle * unicycle; unicycle=new vehicle; /***************** found *****************/ unicycle.message() delete unicycle; unicycle=new car; unicycle-＞message(); delete unicycle; unicycle=new truck; unicycle-＞message(); delete unicycle; }