I'll choose 't' because it's one of the most common consonants in English. With 'e' in the 4th position, this could be a word ending in '-ter', '-ted', '-tes', etc. Common 5-letter words like "water", "later", "noted" all contain 't'. Since vowel 'e' is already found and 'a' has been tried, a common consonant is the logical next choice.