The sublime second movement from Mozart's Clarinet Concerto K.622 (used to great effect in "Out of Africa"). The tune passes seamlessly between the parts, with the alto flute even getting a short cadenza.
Performance duration (approx): 4'50
Difficulty guide: 6-8
Difficulty level, roughly compared to ABRSM exam grades. 0 is total beginner, 9 is advanced (beyond grade 8).