The current pattern is r__t__, and the guessed letters include a, e, o, r, t. Considering that vowels a, e, and o are already guessed and did not appear (r and t are in place), one possibility is that the word may not contain many common vowels. A 6-letter word that fits this pattern is 'rhythm' (r-h-y-t-h-m). With 'rhythm' in mind, the letter 'h' is a strong candidate (appearing twice in the word). I'll guess 'h'.