, I think, and the problems could be settled.

A．If you double your efforts                           B．A bit more efforts

C．Making greater efforts                                 D．So long as you keep up your spirits

______________, I think, and the problems could be settled.

___, I think, and the problems could be settled.

___________, I think, and the problems could be settled.

A．A bit more efforts                                       B．Making greater efforts

C．If you double your efforts                                  D．So long as you make more efforts

________, I think , and the problems could be settled.

[　　]

A．If you double your efforts

B．So long as you keep your spirits

C．Making greater efforts

D．A bit more efforts