our friends are excepted to assume the burden of their own defense,_ they are computer to do.
问题描述：
our friends are excepted to assume the burden of their own defense,_ they are computer to do.
A which we are certain B that we are certain of C of which we are sure D for which we are sure
答
选C,根据短语we are sure of it还原句子答案给的是A,搞不懂查了牛津高阶字典，be sure of sth 是 对…有信心 的意思，用在这里不恰当。因为 they are computer to do 是拥有一套完整的主谓结构，就缺少宾，所以用which指代 to do 的那件事情，which we are certain （that）省略了that