The correct syntax for a function prototype within the scope…

The correct syntax for a function prototype within the scope of a class definition that allows us to overload the stream extraction operator >> is ____.   A.  istream& operator>>(istream&, className&);   B.  const istream& operator>>(istream&, className&);   C.  friend operator>>(istream&, className&);   D.  friend istream& operator>>(istream&, className&);