Everyone has his or her advantages and only you do best can help to reach the goal and

问题补充：

Everyone has his or her advantages, and only you do best can help to reach the goal and truly make a difference.

A. discovering what

B. discovering whose

C. by discovering what

D. by discovering which

答案：

(答案→)A. discovering what

B. discovering whose

C. by discovering what

D. by discovering which

解析：discovering what...动名词短语作主语，what引导宾语从句又在从句中作宾语。