you havent started yet, but you want me to give you a single letter word, which only has 2 options to begin with? i dont know if i should give it up that easily.
no, sorry, youre gonna have to at least start the puzzle before i give anything away. but heres what i will do for you. ill give you a hint on what things to consider to figure it you yourself.

[O and W are either A or I, because theyre both one letter words. plug in both possabilities for W in the word WHH. as far as i know, only one of them can work when followed by a double letter.]
there, thats 3 letters right off the bat. read my tutorial in a previous post if youre still having trouble. come back to me later if you really get stuck.