执行下列程序的输出结果是（       ）。
#include
int main(void)
{
       int a = 100, x = 10, y = 20, m = 5, n = 1;
       if (x < y)
              if (y != 10)
                     if (!m)
                            a = 1;
                     else
                            if (n) a = 10;
       printf("%d\n", a);
       return 0;
} A.

10 B.

0 C.

1 D.

100