Who did you see there?
Who did you give the book to?
RULE XVII.
When a relative pronoun is of the interrogative kind, it refers to the word or phrase containing the answer to the question for its subsequent, which subsequent must agree in case with the interrogative; as, "Whose book is that? Joseph's;" "Who gave you this? John."
NOTE. Whether the interrogative really refers to a subsequent or not, is doubtful; but it is certain that the subsequent should agree in case with the interrogative.
FALSE SYNTAX.
Who gave John those books? Us. Of whom did you buy them? Of a bookseller, he who lives in Pearl street.
Who walked with you? My brother and him.
Who will accompany me to the country? Her and me.