Select the most appropriate article to fill in the blank. We visited ______ Louvre when we were in Paris.

Correct option is B

Use "the" before names of specific, well-known buildings or monuments like “the Louvre.” It is a specific and globally recognized place.
Explanation of options: (a) ✘ 'a Louvre' is incorrect for a known location. (b) ✔ 'the Louvre' is correct for famous places. (c) ✘ 'an Louvre' is grammatically incorrect. (d) ✘ Article is required; "the Louvre" is standard usage.