Bonjour !
Pierre : Parle doucement, s'il te plaît !
Are you asking who is Pierre talking to ?
Pierre is talking to his friend.
A- his parents = parlez (vous plural 2nde pers. plural)
B- his teachers = parlez (vous plural + formal 2nde p. plural)
C- his friend = tu (2e pers. sing.)
D- his neighbors = parlez (2de pers. pluriel)
hope this helps ☺☺☺..