This question tests your understanding of verb tenses and modal verbs to express planned actions that changed.

The conversation is about a planned operation that was supposed to happen this month but has now been postponed to next month.

Let's analyze the options:

• Will: This indicates a future action. However, the sentence refers to a past plan ("he is going to have it next month" confirms the plan changed).
• Was to: This structure ("was to + have + past participle") is used to talk about a planned action in the past that did not happen as intended. It perfectly fits this context.
• Used to: This refers to a past habit or repeated action, not a single planned event.
• Needs to: This expresses necessity or obligation, not a changed plan from the past.

Therefore, the correct phrase to complete the sentence is "was to", forming "he was to have had it this month". This means it was arranged or planned for him to have the operation this month, but that plan did not materialize.

Related Concept: The "Was/Were to + Have + Past Participle" Structure

This is a specific grammatical structure used to indicate a past plan, intention, or arrangement that was expected to happen but ultimately did not occur. It often implies that the outcome was different from what was originally intended.

Formula: Subject + was/were + to + have + past participle

Example: "I was to have started my new job yesterday, but the offer was delayed." (The plan was to start, but it didn't happen).

Related Formulae and Theory

Other ways to express unfulfilled past plans:

• Was/Were going to: "He was going to have it this month." (Also correct, but slightly less formal than "was to have had")
• Had been supposed to: "He had been supposed to have it this month."