Select the most appropriate word or phrase to complete the following…

The correct answer is Option (1) → are settled

Tense in a time clause about the future:

• A time clause begins with once, when, after, before or as soon as.
• When the main clause is about the future, the time clause takes the present tense, not "will".
• This sentence:
  • Main clause: "you will find the work is quite easy" is about the future.
  • Time clause: "Once you … into the routine" therefore needs a present-tense verb.
  • "Are settled" is the present tense of be settled, meaning comfortably used to a new place or routine.
  • Complete sentence: Once you are settled into the routine, you will find the work is quite easy.

Why the Other Options are Incorrect?

Option 2: had settled — Incorrect. The past perfect is used for an action finished before another past action. It cannot go with the future "will find".
Example: By the time we arrived, the dust had settled.

Option 3: settled — Incorrect. The simple past describes a finished past action and does not match the future main clause.
Example: The family settled in Pune many years ago.

Option 4: will settle — Incorrect. "Will" is not used in a time clause after once or when. The future is shown by the main clause alone.
Example: I think the dispute will settle itself in a few days.

Contrast: in a time clause after "once" or "when", the present tense ("are settled") carries the future meaning. "Will" stays in the main clause ("will find").