Final Answer:
Mr. Pontellier had the privilege of quitting their society when they stopped to be entertaining.
Step-by-step explanation:
In the given passage, the context suggests that Mr. Pontellier had the privilege of leaving the company of the parrot and the mockingbird when they ceased to be entertaining. The keyword here is stopped, which fits seamlessly into the context. The sentence structure implies a condition for Mr. Pontellier to exercise his privilege, and this condition is the birds' entertainment value coming to an end. Therefore, the most fitting word to complete the sentence is stopped.
The other options - started, performed, and continued - do not align with the logical progression of the sentence. Mr. Pontellier's privilege is contingent on the birds' behavior, and the opposite of being entertaining would be when they stopped making noise or ceased their entertaining activities. The choice of stopped maintains the coherence and flow of the sentence while accurately conveying the intended meaning.
In summary, the final answer, stopped, is the most appropriate choice as it captures the essence of the sentence by indicating that Mr. Pontellier could leave the company of the birds when they ceased to provide entertainment.