pass an object as a copy

class nurses
{
...
...
}
class shifts
{
nurses _nurses;
shifts(nurses _nurses)
{
this._nurses=_nurses;// here the reference of nurses is assigned not the value.
}
...
...
}
main()
{
var ns=new nurses();
var shfts= new shifts(ns);//I want to pass the ns as copy so the value of ns is not changed after shifts make changes on its copy.


}