是宾语从句。语法：sure表示“无疑的、确信的、有把握的”，指主观上对某事相信无疑，不涉及有无客观根据。在句中作表语。“be sure+不定式”往往表示推测的口气，主语不一定是人，表示“一定会…的”、“必定会…的”。
be sure that例句1、If there was any scandal in that company, you can be sure that Bobby will have clocked it.
那家公司有任何丑闻，博比肯定会知道。
2、You can be sure that our team will win.
我们队准保胜利。
3、You may be sure that Li Ying has a finger in the pie.
你可以肯定李英是参与其事的。
4、You can be sure that I will find you, he vowed.
你要知道我肯定会找到你的，他发誓称。
5、How can I be sure that you are not going to steal my money and blackmail me?
我怎么能相信你不会偷我的钱，敲诈我？
