Music small group of instruments in which each player plays his or her own part is called a/an                a.  choir.      b.  chamber ensemble.      c.  orchestra.      d.  wind ensemble.

A small group of instruments in which each player plays his or her own part is called a B. chamber ensemble.
The difference between a chamber ensemble and an orchestra is in the size - a chamber ensemble is a small group of instruments, whereas an orchestra is a large one. A choir refers to singers, and a wind ensemble is one single type of an instrument played by numerous people.

Ais the correct one.