关于 be sure 的搭配

be sure to do
be sure of sth.\doing sth.
be sure that +从句

be sure of sth / doing sth确信
eg. Can I be sure of a profit if I invest?
我要是投资, 肯定能获利吗?

be sure to do 肯定,一定会
He is sure to go there if he is free tomorrow.
如果他明天有空,他一定会去那里的.

be sure that(that可以省略) + 从句 确信
eg. When you start the engine, be sure that the car is in neutral.你在发动引擎时，一定要让汽车处于空档。

注意
sb be sure that + 从句 是正确的
没有It be sure that + 从句
用的时候要当心
eg. He is sure that his students will pass the exam.
他确信他的学生会通过考试的.

be sure of 意思是“对。。。肯定”例如： i am sure of that . 我可以十分肯定

我怎么知道??