I'm definite about this.

　　我對(duì)這事毫無疑問。

　　You're completely mistaken about Jane.

　　你對(duì)簡(jiǎn)的看法完全錯(cuò)了。

　　He's ignorant about modern technology.

　　他對(duì)現(xiàn)代科技一無所知。