Final answer:
A trio sonata typically involves four musicians: two playing the solo melodic parts and two playing the basso continuo, despite what the name may suggest.
Step-by-step explanation:
The trio sonata is a musical form that was popular in the 17th and early 18th centuries. Despite the name 'trio,' a trio sonata typically requires the performance of four musicians. This is because the sonata is written for two solo melodic instruments and continuo, which usually consists of two instruments (a harmony instrument like a harpsichord, organ, or lute, and a bass instrument like a cello or bassoon). The two continuo players together count as one part, hence the name 'trio' sonata.