Included are the first 8 of the 15 three-part sinfonias.
None are in their original keys; keys were picked to
fit the range of the trombone.  Trombone 1 never goes above
C5, and because of flowing counterpoint, is almost always
quite a bit lower than that.  There are no low Bs in trombone
3, and it moves upward contrapuntally quite a bit, so it could
certainly be played on tenor trombone.  But it of course sounds
best on bass.