Is the trombone made of four tubes?

Answer 1

Let's count them:

1. The mouthpiece is essentially a small bowl and a small tube
2. The top slide is one piece into which is placed the mouthpiece
3. The outside slide is the curved piece that is moved back and forth to change pitch
4. The bottom slide is the piece that connects to the bell section
5. The small part of the bell section connects the bottom slide to the tuning slide
6. The tuning slide allows the player to tune the instrument
7. The final piece in the horn is the tube that flares out to the bell

So, it appears that there are SEVEN tubes that make up the Trombone.