Pretty sure the answer is A
Unique or damaging plate edges cause volcanoes. As the more thick plate subducts, it will dissolve at profundity and the water is driven off, will bring down the liquefying purpose of the overlying mantle wedge, this will make a kind of magma. Volcanic Island Arcs are framed at maritime dangerous plate edges. The hot, light magma, is less thick that the encompassing rock so will ascend to the surface, and will gather underneath the plate that hasn't been subducted. It will then, under expanded weight eject under the ocean. More than thousands of a great many years, it will continue emitting, to shape islands.
