填空题 根据下列程序的执行结果，可以断定划线部分的修饰符应为______。执行结果：
i9a football is created.
a football is created.
i=10
a football is destroyed.
a football is created.
i=20
a football is destroyed.
a football is destroyed.
源程序：
#include＜iostream.h＞
class Football

public:
Football( )cout＜＜"a football is created."＜＜endl;
～Football( )tout＜＜"a football is destroyed."＜＜endl;
;
void func(int i)

______Football f1;
Football f2;
cout＜＜"i="＜＜i＜＜endl;

void main( )

func(10);
func(20);