#include <iostream> using namespace std; class shape {public: virtual int area()=0; }; class rectangle:public shape {public: int a, b; void setLength (int x, int y) {a=x;b=y;} int area() {return a*b;} };若有语句定义rectangle r; r.setLength(3,5); 则编译时无语法错误的语句是( )