The correct response is: The maritime tropical air mass would rise above the continental polar air mass, and thunderstorms would form.
When a maritime tropical air mass (warm and moist) collides with a continental polar air mass (cold and dry), the warmer, less dense maritime tropical air mass will rise over the colder, denser continental polar air mass. This rising motion can lead to the development of storms, including thunderstorms, as the warm, moist air cools and condenses.