几道名词性从句的题目.求答案和分析

几道名词性从句的题目.求答案和分析
1、It was ＿＿he worked hard that he succeeded.
A.because B.since C.as D.for
2、His suggestion ＿＿ to see the art exhibition interested everyone of us.
A.that we go B.that we would go
3、Are you sure＿＿?
A.whether she is honest B.that she is honesty
C.she is honest D.is she honest