Wind power is an ancient source of energy        we may return in the near future.

Wind power is an ancient source of energy ____we may return in the near future.

Wind power is an ancient source of energy        we may return in the near future.

Wind power is an ancient source of energy        we may return in the near future.

A．on which          B．by which          C．to which          D．from which

 Wind power is an ancient source of energy ____we may return in the near future.

A．on which                              B．by which

C．to which                              D．from which

Wind power is an ancient source of energy        we may return in the near future.

A．on which          B．by which          C．to which          D．from which

Wind power is an ancient source of energy ___________ we may return in the near future.

Wind power is an ancient source of energy _____ we may return in the near future.

A. to which        B. by which      C. from which       D. on which

Wind power is an ancient source of energy ________ we may return in the near future.

    A. in which         B. to which         C. on that      D. from which

Wind power is an ancient source of energy        we may return in the near future.

A. on which       B. by which          C. to which                D. from which