B: sediments melt deep beneath earth's surface
I guess the "mekong" river.
Answer:
At convergent point of plate boundaries, sedimentary rock that is present at ocean floor is pushed down into mantle. Due to the continuous movement of rock into the mantle increase the crust the temperature. Thus after continuous rise of temperature, crust melts down and eventually rise to surface of earth in the form of volcanic eruption. and after cools down gives rise to formation of igneous rock.
Explanation:
Process of igneous rock is given below
At convergent point of plate boundaries, sedimentary rock that is present at ocean floor is pushed down into mantle. Due to the continuous movement of rock into the mantle increase the crust the temperature. Thus after continuous rise of temperature, crust melts down and eventually rise to surface of earth in the form of volcanic eruption. and after cools down gives rise to formation of igneous rock.