The scientist's discoveries were of           great help to           mankind．

A．a；the                 B．a；／                  C．／；／                D．the；the

The scientist's discoveries were of ____________great help to ____________mankind．

A．a；the          B．a；／           C．the；the        D．／；／

 The scientist's discoveries were of           great help to           mankind．

A．a；the           B．a；／            C．／；／           D．the；the