Choose the option that best completes the sentence using an appropriate…

Concept: A concessive conjunction — "though", "although", "even though" — marks the clause it introduces as a reason to expect one thing, while the other clause states something you would NOT have expected from it. The conjunction adds no content of its own; it only announces that a stated expectation is about to be overturned. So in a fill-in-the-blank of this kind, the correct word is the one that makes the main clause run COUNTER to the expectation the concessive clause sets up. The test is not what the word means in isolation, but whether the finished sentence still overturns an expectation.

Application: The concessive clause here is "Though unfamiliar with the topic". Ask what unfamiliarity ordinarily leads a listener to expect about the MANNER of someone's answering: it predicts an unsure manner — pausing, guardedness, unease. The blank sits in the main clause and describes exactly that manner, so to give "Though" something to overturn it must name a manner of answering that a listener would NOT expect from an unfamiliar speaker: answering with self-assurance in spite of not knowing the topic.

Why grammar alone does not decide it: all four adverbs yield a grammatically well-formed English sentence, so grammaticality cannot be the test — and the stem accordingly asks for the option that BEST completes the sentence. The deciding question is whether the finished sentence still overturns an expectation. If the manner adverb names something a listener would already have expected from unfamiliarity, no expectation is overturned and "Though" is left with nothing to concede: the sentence stops making the point the conjunction set it up to make.

Cross-check: each adverb tested against the expectation "Though unfamiliar with the topic" sets up:

• confidently — names self-assurance, which is the direct opposite of the unsure manner unfamiliarity predicts, so the expectation is overturned and "Though" does its job.

• hesitantly — names doubt-driven pausing, which is precisely the manner unfamiliarity predicts, so the expectation is confirmed rather than overturned.

• cautiously — names deliberate care taken to avoid a mistake. Care is not in itself the opposite of assurance — a well-prepared speaker can be careful too — but it is still a manner a listener would readily expect from someone on unfamiliar ground, so nothing is overturned.

• nervously — names anxious tension. Anxiety is not in itself a measure of assurance either, but it is likewise a manner unfamiliarity would lead a listener to expect, so again nothing is overturned.

Result: Only one of the four adverbs describes a manner of answering that "Though unfamiliar with the topic" would NOT lead you to expect — the adverb of manner meaning "with self-assurance". The sentence reads: "Though unfamiliar with the topic, he responded to the questions confidently."