?确信

... true 符合客观事实的（人和事） really 真实存在的（人和事） be sure that 确信... I don't think (that)...我不认为...（否定前置）GF宾语从句 ...

?从句

... be sure to do sth. 对做某事有把握 be sure that 从句 确信 float away into space 飘走进入太空 ...

?确定

... be sure that 确定…… be central to ……的核心 involve with 使……卷入；与……有关 ...

?要确保

... horoscope ? 星座 be sure that ? 要确保 Nobody knows who I really am ? 谁也不知道我到底是谁 ...