下列程序的运行结果是 【15】 。
#include＜iostream, h＞
class Sample

int a;
public:
Sample(int aa=0) a=aa;
～Sample() cout＜＜"Sample="＜＜a＜＜;
class Derived: public Sample

int b;
public:
Derived(int aa=0, int bb=0): Sample(aa) b=bb;
～De rived() cout ＜＜"Derived="＜＜b＜＜’’;
void main()

Derived dl (9)

顺线路行走时有何规定？