Meaning: 'Response' refers to an answer or reaction to something, in this case, the holiday cards sent by the professor.

Wrong options:

• bitterness: 'Bitterness' refers to a feeling of anger or resentment, which does not fit the positive context of receiving holiday cards.
• agony: 'Agony' denotes extreme physical or mental suffering, which is unrelated to the context of receiving holiday greetings.
• pique: 'Pique' means to stimulate interest or curiosity, but it does not convey the idea of a reply or reaction, making it unsuitable here.

Correct answer: addressed

Explanation: The word 'addressed' is the past participle of the verb 'address,' which fits grammatically as it describes the action taken on the holiday cards that were sent back. It aligns contextually with the idea of the cards being directed to the professor.

Meaning: 'Addressed' means that the cards were labeled with the professor's name and sent to him, indicating they were meant for him.

Wrong options:

• captured: 'Captured' implies taking hold of something, which does not relate to the context of sending cards back to someone.
• rancor: 'Rancor' refers to bitterness or resentment, which is not relevant to the act of sending holiday cards.
• petulance: 'Petulance' denotes a state of being irritable or sulky, which does not fit the positive context of holiday greetings.

Correct answer: into

Explanation: The preposition 'into' fits grammatically and contextually as it indicates the direction of inquiry regarding the identity of the professor. It suggests a deeper investigation, which aligns with the context of curiosity about someone unknown.

Meaning: 'Into' in this context means to inquire about or investigate something, specifically the identity of the professor.

Wrong options:

• for: 'For' typically indicates purpose or reason, which does not convey the idea of investigating someone's identity.
• of: 'Of' suggests belonging or association, which does not fit the context of asking about someone's identity.
• with: 'With' implies accompaniment or association, which does not convey the idea of inquiry.

Correct answer: reciprocation

Explanation: The word 'reciprocation' fits grammatically as a noun that describes the act of returning a favor or gesture. It is contextually appropriate as it relates to the concept of returning kindness, which is the main theme of the passage.

Meaning: 'Reciprocation' refers to the act of responding to a gesture or action with a similar one, emphasizing the social norm of returning favors.

Wrong options:

• desolation: 'Desolation' refers to a state of complete emptiness or destruction, which is unrelated to the concept of returning favors.
• poignancy: 'Poignancy' denotes a quality that evokes a keen sense of sadness or regret, which does not fit the positive context of returning kindness.
• hostility: 'Hostility' indicates unfriendly or antagonistic behavior, which is the opposite of the cooperative spirit described in the passage.

Correct answer: sure

Explanation: The word 'sure' fits grammatically as an adverb that expresses certainty, aligning with the context of inviting someone to a party. It conveys a strong intention to reciprocate the invitation.

Meaning: 'Sure' means certain or confident, indicating that one should definitely invite the couple to their own party.

Wrong options:

• might: 'Might' suggests possibility but lacks the certainty required in the context of reciprocating an invitation.
• well: 'Well' is often used as an adverb for manner but does not convey the certainty needed in this context.
• try: 'Try' implies an attempt but does not express the assurance that one should invite the couple, making it less fitting.