to speak at the meeting?

I don't know the professor to speak at the meeting now is from south.

为什么要有一个to呢？
这个事属于哪方面的语法问题啊？ 不好意思，我没见过to是可以修饰其他成分。

还有，如果没有后面的 is from south 那么这个 to 是否就要省略呢？
是否改为
I don't know the professor who is speaking at the meeting now.
（这个Who 是否正确？）

to可以修饰句子么？ 我能在语法书的那一部分得到印证？

That was the reason ____David refused to speak for at the meeting. _____ of the boys is going to speak at the meeting this afternoon.(each or every) That was the reason__ Mr Smith refused to speak for at yesterday's meeting lily,there ie someone at the front desk____(A,who B,which ,C,whom)would like to speak with you to speak is the sin是什么意思? It is right to speak the truth. looking for the partners to speak English unless_____to speak.You should remain silent at the conference. take ()to the right at the corner she dropped the tray when i _____(speak)to her