The result of the survey showssuccessful people have in common isthey all have confidence.

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A. whether; that
(答案→)B. what; that
C. what; why
D. which; that
解析：考查名词性从句，第一空填what，引导宾语从句，在宾语从句中what做have的宾语。Have sth in mon是“和…有共同之处”，第二空填that，引导表语从句，that指起到连接作用，不做成分，句意是：调查的结果显示，成功的人共有的东西是他们都很自信。选B。