单选题 有如下程序：
#include＜iostream＞
#include＜string＞
using namespace std;
class Person
public:
Person(string n):name(n)cout＜＜'P';
pnvate:
string name;
;
class Date
public:
Date(int y=2012,int m=12,int d=21):year(y),month(m),day(d)cout＜＜'D';
private:
int year,month,day;
;
class Student:public Person
public:
Student(string n,int y,int m,int d,char c):birthday(y,m,d),sex(c),Person(n)cout＜＜'S';
private:
Date birthday;
char sex;
;
int main()
Student stul("Zhang",1990,10,1,'F');
return 0;

运行时的输出结果是______。
A．S B．PS C．DPS D．PDS