Why A? And why not the others?

Correct answer: A. France

France spans twelve time zones once its overseas departments and territories are counted — from French Polynesia and Wallis and Futuna in the Pacific to Réunion in the Indian Ocean and the French Southern and Antarctic Lands — the most of any country on Earth, even though mainland France itself sits in a single zone. Russia is the classic near-miss: despite being the largest country by land area and widely assumed to be the record-holder, it uses eleven time zones, one fewer than France. The United States and the United Kingdom both hold overseas territories too, but theirs are clustered across fewer longitudes, so each covers noticeably fewer zones than either France or Russia.

Source: Britannica: France (overseas departments and territories); CIA World Factbook: France