C程序，单链表尾插法报Access Violation错

Question

struct Person
{
char name[40];
char phone[20];
struct Person *next;
};

void input(struct Person *person)
{
printf("请输入姓名：");
scanf("%s",person->name);
printf("请输入号码：");
scanf("%s",person->phone);
}

void addPerson(struct Person **person)
{
struct Person *add=NULL;
static struct Person *tail;
add=(struct Person *)malloc(sizeof(struct Person));
if(add==NULL)
{
printf("内存分配失败！");
exit(1);
}

input(add);

if(*person!=NULL)
{
tail->next=add;
add->next=NULL;
}
else
{
*person=add;
add->next=NULL;
}
tail = add;
}
int main(void)
{
struct Person *person;
int ch;
printf("是否录入数据？（输入-1结束录入）")
scanf("%d",&ch);
while(ch!=-1)
addPerson(&person);
return 0;
}
运行了以后会报错Access Violation，提示是addPerson()函数的tail->next=add;语句有问题，有没有大佬能解答一下

Answer 1

为什么 add=(struct Person *)malloc(sizeof(struct Person));知道申请内存，tail就不知道申请内存？