This is a past paper of a national test in Thailand. (Manee is a common Thai name and Songla is a province). The answer to this question is (4)How have you been? But I wonder why (3)How do you do? is wrong. I think I can just fill in any greeting so (3) and (4) are both correct.
So is (3)How do you do? okay for this question? and what is the difference between those two?