Which of these is a form of early black music used by vocalists when they improvise?
O A. work songs
O B. hard bop
O C. New Orleans jazz
O D. swing

The answer is A

explaination:

whenever slaves would be sent to work on a plantation they would sing work songs to help let time pass

pitch- the definition of pitch is as follows:

"the quality of a sound governed by the rate of vibrations producing it; the degree of highness or lowness of a tone."