Grammar Problems from a Senior in High School

This evening, my niece asked me to teach her English grammar. The following is what had confused her:

1. Wh-noun clause

e.g. Where is John?

--> I don't know where John is.

Where does he live?

--> I don't know where he lives.

She couldn't understand why the noun clause doesn't have the question structure. I told her the wh-noun clause is no longer a question, but a part of a sentence, serving as the object of the verb "know." Since the clause itself is not a question, it doesn't need inversion of the subject and the verb.

2. The relative pronoun "whom" and when not to use "that" as a relative pronoun.

3. The relative pronoun "which" used to modify a clause.

e. g. Tom was late, which made the teacher angry.

My niece asked me why we can't use "it."  My answer: Using it, we make the mistake of having two verbs in a simple sentence. "Which"in a relative clause is not only a pronoun but a conjuction, used to connect two clauses and therefore making the sentence right.

4. "one of whom," "some of which"

e.g. I have three sisters, two of whom are in the States.

5. The restrictive and the non-restrictive adjective clause.

e. g. Our professor who teaches Chemistry 101 is an excellent lecturer.

Prof. Wilson, who teaches Chemistry 101, is an excellent lecturer.  (These two examples are from her grammar book: Azar.)