I'm choosing 't' because it's one of the most common consonants in English words. With a 6-letter word that has 'a' as the third letter, there's a good chance 't' might appear, especially at the beginning or end of the word. Common 6-letter patterns with 'a' as the third letter include words like "really", "health", etc., though those specific examples don't have 't'. Still, 't' is a high-frequency letter that would be valuable to check.