Fill in the blank with a suitable 'Question Tag' for the given senten…

The correct answer is Option (2) → don't they?

Question tags:

• A positive statement takes a negative tag, and a negative statement a positive tag.
• The tag uses the statement's helping verb. If there is none, it uses do/does/did in the same tense.
• The tag's pronoun matches the subject: "the scuba divers" → they.
• This sentence: "need" is a main verb here (need + noun "air cylinders"), in the simple present, plural subject, positive statement → don't they?
• Complete sentence: The scuba divers need air cylinders, don't they?

Why the Other Options are Incorrect?

Option 1: do they? — Incorrect. A positive tag after a positive statement breaks the rule. The tag must be negative.

Option 3: need they? — Incorrect.

• "need" is a main verb with an object here, so the tag takes do, not need.
• The tag is also positive after a positive statement.

Option 4: needn't they? — Incorrect. The tag is negative, but "needn't" treats need as a modal. With "need + noun" the tag uses don't.