It's B. Just 21 days earlier the British had marched into Washington and burned the place to the ground. (It was specific British retaliation for U.S. forces having burned the equivalent of the Canadian white house to the ground the year before.) It was a humiliating and very embarrassing loss. Here we were, this growing stronger every day new proud country, and we couldn't even defend our own capital. So, after that fiasco, the country needed a win - any win - to turn things around and get morale back up again. They found 3 such wins that were all milked from the activities associated with the follow-on battle of Baltimore three weeks later. The first win was that the British ground force commander, Major General Ross, was killed by an American sharpshooter at a skirmish at North Point. This deprived the British of their most important infantry leader. Then, overall U.S. troop strength was higher and tougher than the British expected, so their ground troops pulled back to their ships in the harbor. Next, every ship in the British fleet in the harbor fired every gun they had at our Fort McHenry, which was guarding the port. The British fired for 27 straight hours, basically until they ran out of ammunition. Seeing they had not done much damage to the fort and out of ammo, the British had to pull back to Bermuda and New Orleans for resupply. This was the second win for the U.S. The last and final win was Francis Scott Key seeing the American flag still flying above Ft. McHenry after the bombardment. He was so moved by it that he wrote the lyrics to the Star Spangled Banner which within a matter of weeks had been published in every newspaper across the country. Once published, it similarly moved all other Americans too, and of course is with us to this very day.
The answer can't be A by the way, because the first American land victory of the war had already taken place 2 years earlier with the successful defense of Fort Harrison in Indiana.
