不定式与被修饰的名词,如果能够构成逻辑上的主谓关系,就不要加介词,否则,就必须加上一个合适的介词.
例:1.I have a room to live in.我有一间房子住.
可变为:I live in a room.(如果去掉介词in,句子明显不通.因为live为
不及物动词)
其他,如:I have a pen to write with.
He has many friends to talk to.
2.I have some bread to eat.
可变为:I eat some bread.(eat本身就是及物动词,不需要加介词)