The area labeled B is called what? 1. rift valley
2. trench
3. mid-ocean ridge
4. subduction zone

its subduction zone

Explanation:

Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the heavier plate dives beneath the second plate and sinks into the mantle.

answer at the divergent plate boundary in the middle of the ocean;