I believe you have made efforts and you are sure to achieve your goal.
A. that; /
B. /; /
C. /; that
D. whether; that
网友回答
A. that; /
B. /; /
(答案→)C. /; that
D. whether; that
解析：考查宾语从句的连接词：句意：我相信你已经努力了，而且你一定能达到目标。Believe后面接了两个宾语从句，都是用that引导，第一个可以省，第二个就不能省略了，选C。