There are two common types in page replacement algorithm: stack and non-stack strategies. When a real page number increase only stack algorithm can increase the hit rate monotonously. In the following replacement algorithm, which one belongs to non-stack strategy( ).

A．FIFO

B．LRU

C．PFF

D．OPT

以下程序的输出结果是______。
int fun(int*x,int n)
if(n==0)
return x[0];
else return x[0]+fun(x+1,n-1);main()
int a[]=1,2,3,4,5,6,7;
printf("%d\n",fun(a,3));