单项选择题

有以下程序：
class Date

public:
Date(int y, int m, int d);
year = y;
month = m;
day = d;
Date(int y = 2000)
year = y;
month = 10;
day = 1;
Date(Date &d)

year = d.year;
month = d.month;
day = a.day;

void print()
cout＜＜year＜＜"."＜＜month＜＜"."＜＜day＜＜end1;

private:
int year, month,day;
;
Date fun(Date d)
Date temp;
temp = d;
return temp;

int main()

Date date 1 (2000,1,1),date2(0,0,0);
Date date3(date 1);
date2 = fun(date3);
return 0;

程序执行时，Date 类的拷贝构造函数被调用的次数是

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