1) The first three sentences ask questions. They should end with a question mark. 2) To be strictly correct, a traditional grammar rule say that the first two sentences should use the form "whom," because the pronoun is the object of the sentence. However, this rule is often ignored. 3) In the present tense, the third person singular form of a verb ends in an "s." I teach, you teach, he teaches, she teaches, we teach, they teach. 4) The fourth sentence is different from the others. It isn't a question. It means that the class he teaches is very interesting. It is more interesting than other classes. It's a strong statement, and an exclamation point might be appropriate. Thus: your sentences should be: Whom did you see? Whom did he paint? Who yelled? What an interesting class he teaches!