单选题 以下程序运行后的输出结果是( ). #include <stdio.h> #include <stdlib.h> struct NODE { int num; struct NODE *next; }; int main() { struct NODE *p,*q,*r; p=(struct NODE*)malloc(sizeof(struct NODE)); q=(struct NODE*)malloc(sizeof(struct NODE)); r=(struct NODE*)malloc(sizeof(struct NODE)); p->num=10;q->num=20;r->num=30; p->next=q;q->next=r; printf("%d\n",p->num+q->next->num); return 0; }