C. Feature A is an abyssal plain and Feature B is an ocean trench
Abyssal plain, flat seafloor area at an abyssal depth (3,000 to 6,000 m [10,000 to 20,000 feet]), generally adjacent to a continent. These submarine surfaces vary in depth only from 10 to 100 cm per kilometre of horizontal distance.
Oceanic trenches are topographic depressions of the seafloor, relatively narrow in width, but very long. These oceanographic features are the deepest parts of the ocean floor.
