careful的比較級是more careful,最高級是the most careful。careful的意思是小心;注意;謹慎;細致的;精心的;慎重的，carefully 是它的副詞形式。

例句：

Can't you be a bit more careful with my bike？你騎我的車就不能更小心點嗎？

Such an occasion demands the most careful consideration。這樣的場合需要最周到的考慮。

We all think he is one of the most careful students in his class。我們都認為他是班里最細心的學生之一。