I think and all the problems could be settled.A. If you make more effortsB. Making more

问题补充：

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

A. If you make more efforts

B. Making more efforts

C. A bit more effort

D. To have made more efforts

答案：

A. If you make more efforts

B. Making more efforts

(答案→)C. A bit more effort

D. To have made more efforts

解析：选C。句中有并列连词and，故应选择C项。其中名词短语相当于一个祈使句，完整的句子为：Make more efforts, I think, and all the problems could be settled.如选A , and要删去。