分析一下这段程序的输出：

class B
{
public:
B()
{
cout<<"default constructor"<<endl;
}
~B()
{
cout<<"destructed"<<endl;
}
B(int i):data(i)    //
{
cout<<"constructed by parameter " << data <<endl;
}
private:
int data;
};

B Play( B b) 
{
return b ;
}

int main(int argc, char* argv[])      
{                                    
B t1 = Play(5); 

B t2 = Play(t1);    
return 0;  
}