Can we just go back a step with this - I'm not as quick as you guys and I'm not happy about trying to guess the key phrase. Using the US=TE, ET=?S knowns, the line/column SE?UT works? If so, it must form part of the key?
And going back to KT's conundrum, let's say there's a row SE?UT. As long as D is in the same column as T, and D is in the same column as U, DU=GT should also work?