Final answer:
The statement that 'The only function of a jazz drummer is to keep the time and groove.' is not true. Jazz drummers have a multifaceted role within a jazz ensemble. Moreover, to make a drum sound lower in pitch, a drummer should loosen the drum skin.
Step-by-step explanation:
The question asks which of the following statements about jazz drummers is not true. The incorrect statement is: b) The only function of a jazz drummer is to keep the time and groove.
This statement is not true because jazz drummers do much more than just keep time; they interact with soloists, contribute to the ensemble's sound, and adapt to the evolution of jazz.
Regarding the specific task of adjusting the pitch of a drum, the correct action for a drummer would be to: d) loosen the drum skin.
This is because tension on the drumhead directly affects the pitch of the sound produced. Loosening the drum skin reduces the tension, which results in a lower pitch, while tightening the drum skin increases the tension and raises the pitch.