Choose the most appropriate option to fill in the blanks in the given…

The correct answer is Option (2) → (a) and (b) as though

Conjunctions of addition and manner:

• And joins two actions of the same subject done one after the other: he rubbed his eyes and yawned.
• As though (= as if) describes the manner of an action by comparing it with an imagined situation; it can be followed by a clause or, as here, by an -ing phrase.
• This sentence: he rubbed his eyes and yawned in the way a person does when waking up after a long sleep.
• Complete sentence: He rubbed his eyes and yawned as though waking up after a long sleep.
  Example: She looked at me as though she had seen a ghost.

Why the Other Options are Incorrect?

Option 1: (a) after (b) but — Incorrect.

• "after yawned" is not English; "after" needs a noun, an -ing form or a full clause ("after yawning", "after he yawned").
• "but" shows contrast, and there is nothing to contrast here.

Option 3: (a) for (b) or — Incorrect. "For" (meaning because) cannot join a verb like "yawned" without a subject, and "or" offers a choice where none exists.

Option 4: (a) nor (b) or — Incorrect. "Nor" adds a negative and needs a negative before it (neither ... nor, not ... nor); the sentence is positive.