Consider the sentence below.

"By the time the inspectors arrived, the team had been testing the system for three hours, and they have since revised the protocol twice."

The forms establish different temporal reference points rather than merely identifying past and present events.

Analyze the statements below.

I."Had been testing" represents an activity already in progress before the inspectors arrived and emphasizes its preceding duration.
II."Have since revised" relates subsequent revisions to a period extending to the speaker's present reference point.
III."Arrived" establishes an event that occurred before the beginning of the testing process.

It is CORRECT what is stated in: