改错题使用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 messageCar messageVehicle message源程序文件test17_1.cpp清单如下：#include 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; }
dx=（）。