Question

The deepest portions of the ocean are part of the relatively narrow features called submarine canyons

Answer 1

Even though the submarine canyons are very steep and deep parts of the oceans, and can go up to 5 km in depth, still they are not the deepest parts of the oceans. The deepest parts are were there's two plates moving away from each other and making huge gaps, like in the case of the deepest place on the planet, the Marian Trench, with around 11 km depth.