1. describe a mandolin, banjo, or dobro. describe its appearance, construction, sound, and unique qualities and how it is used musically.

A mandolin is an eight stringed instrument. The body is made of wood and the tuning is usually the same as a violin (GDAE). Mandolins are commonly played in bluegrass type music.
A banjo has 4 or 5 strings. Most commonly it is tuned in a G chord, although it is also tuned in other chords. The body is made with the same material as the top of a drum with a kind of metalic sound. Banjos are commonly played in bluegrass music.
I have no idea what a Dobro is, but I play both the mandolin and banjo so I know those answers are accurate.