The professor can hardly find sufficient grounds         his argument.

A．which to be based on                         B．on which to base

C．which to be based                      D．which to base

The professor can hardly find sufficient grounds          his argument in favor of the new theory.

A．which to base on                                        B．on which to base

C．to base on which                            D．which to be based on

The professor can hardly find sufficient grounds　 ________ his argument in favor of the theory.

A．which to base on　　 B．on which to base

C．to base on which　　 D．which to be based