Be careful with强调的是对干什么要认真,谨慎
例句：You must be careful with that vase,it is ver fragile.
你要小心对待那个花瓶,因为它很易碎
Be careful abou强调的是要当心、小心,对..提高警惕
例句:Everyone should be careful with fire when using it.每个人都应该谨慎用火
Be careful in用法和be careful with用法近似
Be careful of强调对...认真,细心,小心（比较褒义）
例句：You are very careful of your work.你对你的工作很谨慎/认真
It is really careful of you 你很认真（褒义）