What is a unit of form, such as a mark, shape, line, color, etc

Hurrywhat best describes an a. instruments that produce a sound through vibrating column of air, including the woodwind and brass family.b. simple, solid instruments that produce sound by being struck, scraped, or shakenc. instruments that produce sound by striking or rubbing a skin or membrane stretched across a resonating air chamberd. instruments that produce sound when a string or chord is struck, rubbed, or plucked