A, because all the other are in direct reference to something
The pronoun for the sentence is D.object
Glad to help you ^-^
One example would be<span> me, the other lifeguards, and the swimmers.
Under categories of Agencies, pentad refers to The group of people or the organization that committed to a certain action within a certain environment
In a swimming pool, lifeguards, customers, and swimmers are the group of people that doing the action.</span>