Given the clues and feedback, letters C, R, A, N, E, B, O, T, S, F, U, I, and D are eliminated. The only confirmed letter is L, which must appear but not in positions 2 or 3. With most vowels eliminated, Y is our only viable vowel. 'LYMPH' (L-Y-M-P-H) uses allowed letters, places L in position 1, and is a valid 5-letter word. This guess tests a combination of remaining letters.