I'm not sure she believes me. She probably just thinks I've gone off the deep end.

　　我不確定她是不是相信我。她可能只是覺得我神志不清了。

　　I'm not sure whether I should tell you this.

　　我拿不準該不該把這事告訴你。

　　I'm not sure that this is the most valuable use of my time.

　　我不能肯定我的.時間這樣來安排最有價值。

　　I think this is their house, but I'm not sure.

　　我想這是他們家，但不敢肯定。

　　One should never criticize if one is not sure of one's facts.

　　一個人如果對自己掌握的事實沒有把握，就絕不該隨便批評。