Answer: Volcanoes form at B when the oceanic plate is subducted, and the plate melts and forms magma. This magma rises towards the surface and erupts as lava which forms the volcanoes. It can be found in Pacific Northwest in northern CA, Oregon and Washington. The boundary in B shows converging plate boundary. An oceanic plate collides with a continental plate. The result is the oceanic plate sinks below a deep ocean trench into the mantle. The boundary shown in A is a diverging plate boundary. 2 oceanic plates diverge to form a mid-ocean ridge.
Exceptions to A and B are when volcanoes form at hot spots in the middle of continental or oceanic plates. Magma melts through the crust and moves to the surface in a hot spot. Also a collision between two oceanic plates can form volcanoes. One of the oceanic plate is subducted which melts the plate and the formation of magma which erupts to form a chain of volcanic islands called an island arc.
Explanation: I took the test and aced it so i hope this helped
