Final answer:
On an Airbus A321, boarding PA announcements are typically made by the captain or first officer, or they may also be made by the cabin manager; ground crew are not responsible for in-flight communications.
Step-by-step explanation:
On an Airbus A321, the responsibility for making the boarding public address (PA) announcement can vary by airline. However, typically, the captain or first officer makes important announcements, while flight attendants or the cabin manager may also make general boarding announcements. The boarding PA is usually not made by the ground crew, as they are not responsible for in-flight communications.