Explanation

If Denise looks distant, it appears that she is unaware of her surroundings. Truant means absent, which makes no sense in this text, and fetching means attractive, which is also irrelevant. Her distant look makes her appear oblivious, or unaware.

The word actually signals that the second blank must go in a different direction from the first, and must mean something such as aware. Sedulous means hardworking, which has nothing to do with being aware. Insensible means unaware, and is the opposite of what you’re looking for. Cognizant means aware, and is the best fit for the second blank.

Hence options B and F are correct!
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It's bizarre that the sentence itself does not provide the clue(s) to figue out the real answers without watching out the given answers.
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Plugging options is always a good strategy
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