to be careful是修饰tell,还是后面的介词短语

Then you must tell him to be careful about what he says.

Then you must tell him ，to be careful，about what he says.

Then you must tell him about what he saysto be careful.

Then you must tell him about what he says,to be careful.

老师，几个句子有哪些不同，第一句：to be careful是修饰tell,还是后面的介词短语？

Then you must tell him to be careful about what he says.

to be careful不是修饰tell, 更不是修饰介词短语。而是tell后的宾语补足语。about what he says 为介词短语修饰表语形容词careful。可以理解为表语形容词的方面状语。

你写的其它三个句子都是不对的，没有相互不同的问题。

建议：多读多记你看到的正确的句子，不要自己去改动句子结构。正确的句子见多了，就渐渐可以辨认什么是不对的结构。