▲Be careful 意为“小心，当心，留意，注意”等，后接介词 of, with, in doing, 动词不定式以及 wh-word 从句等。具体句式是：

1. be careful of

2. be careful with

3. be careful in doing

4. be careful to do

5. be careful +wh-word从句

【例句】

1. Be careful of the dog; it sometimes bites people.  留心那条狗，有时候咬人。

2. These glasses are very expensive so please be careful with them. 这些玻璃杯十分昂贵，因此请小心些。

3. Be careful in dealing with such people. 与这种人打交道要小心谨慎。

4. Be careful to avoid breaking the glass.当心不要打碎玻璃

5. Be careful what you say; even the walls have ears! 说话要小心，隔墙有耳啊！

▲Be careful之后接wh-word引导的从句有很多，如：what, how, where, who, whom等等。理解为be careful的宾语从句，也可以理解为Be careful of中，省略了介词of。

【例句】

1. Also, be careful what you write in an e-mail.而且，你写电子邮件的时候要小心仔细。

2. You must be careful how you start the personal computer. 你一定要注意怎样起动个人电脑。

3. Keep in mind that metal ladders conduct electricity so be careful where you place them.要注意的是，金属梯子会导电，所以在放置梯子的时候要选好位置以确保安全。

4. I don't want to be rude, but we have to be careful who we give this information to.我不是有意无礼，只不过这份资料给谁我们必须很慎重。

5. Be careful whom you associate with.要留心你和什么样的人交往。

▲be careful of与be careful with的区别：

be careful of the thief 当心（留意，警惕）那个小偷。

be careful with the machine 操作机器要小心(仔细)。

▲be careful in doing与be careful to do的区别：

be careful in doing an experiment做试验过程中要仔细小心。（做某事时要仔细小心）

be careful not to wake the baby. 注意别吵醒了宝宝。（不定式表示“注意、留意”的目的）

▲be careful还可接that从句，陈述一个情况：

Be careful that the medicine is kept away from children.要小心把药放在安全的地方,不要让小孩拿到。

Be careful that you are not late for class.注意上课不要迟到。