, 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
网友回答
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。