阅读以下说明和C++程序，将应填入(n)处的字句写在对应栏内。
【说明】
下面程序的功能是计算并输出某年某月的天数，函数IsLeap Year()能够判断是否是闰年。
【C++程序】
# include ＜ iostream ＞
using namespace std;
(1) Month {Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec };
class Date {
public:
Date( int year, Month m_ month) {
this→year = year;
if( (2) ) month: Jan;
else month = m_ month;
};
～Date(){};
bool IsLeap Year( ) {
return ((year%4= =0 &&year% 100 ! =0)｜｜ year%400= =0);
};
int CaculateDays( ) {
switch(m_month ) {
case (3) ;{
if (4) return 29;
else return 28;
}
case Jan: case Mar: case May: case Jul: case Aug: case Oct: case Dec: return 31;
case Apr: case Jun: case Sop: case Nov: return 30;
}
}
private:
int year;
Month month;
};
void main( ) {
Date day(2000,Feb);
cout ＜ ＜day. (5) ( );
}