All blanks require the same letter T to complete valid words: TOMATO, BEST, COW PHOTO, MOTO (or MOTO isn't standard, but MOTTO is). Actually: TOMATO (valid), BEST (valid), COW PHOTO (together makes 'cow photo' or the words COW and PHOTO separately), MO TO (doesn't make sense). Let me re-examine: OMATO = TOMATO, BES = BEST, OW = COW, PHO_O = PHOTO, MO _O could be MOTO? The pattern is that T completes all: TOMATO, BEST, COW, PHOTO. The blanks represent T, T, T, T, T, T respectively.