Explanation

Reading the question: We inhale the prompt. The vice tax has worked in G country, but not in B country, even though the tax did affect the price of nicotine products as planned. Why?, we are asked.

Creating a filter: the question rules out price as an explanation, so the explanation is something other than price. Maybe people in B country love their nicotine products more and are unperturbed by the new prices. Maybe people in B country are richer, although that does touch on pricing in some ways. We imagine that B country is more nicotine-demanding. We can think of our filter for the correct answer is "demand, not price."

Applying the filter: choice (A) doesn't touch on demand, and the tax effects should be unrelated to the variety of products, if they are taxed equally, which we're led to believe. So (A) is out. Choice (B) is out; the mechanism to achieve the effect is irrelevant if the price effect is equal, which we're led to believe. Choice (C) is close to our filter, since it touches on the subject of demand. Prices in B country are up, but increased advertising could help with demand. Choice (D) also concerns demand, so it passes the filter. Choice (E) is out; we don't see any reason to think other vice taxes would affect this vice tax. That leaves us with choices (C) and (D).

Logical proof: we'll find an objective difference between (C) and (D). The prompt has a dramatic phrase: demand for nicotine products remained undiminished. Abundant advertising, in (C), could explain why demand was undiminished across the board--in basically all nicotine-buying and -consuming situations. After-dinner smoking, in (D), could explain why some nicotine consumption would survive, but it doesn't explain demand going completely undiminished. The correct answer is (C).