Which of the following sentences is correct according to English grammar and usage? (Note: this was asked in an examination and I have to select only one of the four sentences.)
1) The fishermen, whom the flood victims owed their lives, were rewarded by the government.
2) The fishermen, to which the flood victims owed their lives, were rewarded by the government.
3) The fishermen, to whom the flood victims owed their lives, were rewarded by the government.
4) The fishermen, that the flood victims owed their lives, were rewarded by the government.
I think it is 1) or 3), but I’m not sure which. Is “to” required before “whom” in a sentence like this?