What type of seafloor landform includes the Mariana, Tonga, and Kermadec examples?

The Mariana, Tonga, and Kermadec examples are oceanic trenches.

An oceanic trench is a long, narrow depression in the seafloor, commonly found where one oceanic tectonic plate bends downward and sinks beneath another plate. These features can reach depths of 10 kilometres or more below sea level and are among the most dramatic structures on Earth.

The Mariana Trench contains Challenger Deep, the deepest known point on the seabed. The Tonga Trench includes Horizon Deep, while the Kermadec Trench reaches roughly 10,000 metres. Tonga and Kermadec form connected sections of a major South Pacific subduction system.

The alternatives describe different landforms. A seamount is an underwater mountain, a mid-ocean ridge is a submarine mountain chain formed at a spreading boundary, and an abyssal plain is a broad, relatively flat deep-ocean region. Trenches are especially associated with convergent plate boundaries, volcanic arcs, and earthquake zones.