The correct answer is - C. A plate is pulled under another plate and melts into the mantle.
The subduction zones appear on the plate boundaries between an oceanic plate and continental plate. The heavier and lower oceanic plate moves under the lighter and higher continental plate, thus subducting bellow it. As the plate is subducting, it reaches the mantle layer, its upper part, and because of the very high temperatures and high pressures, the plate that is subducting starts to melt. As the crust is melting, it is becoming a part of the mantle, thus becoming magma, which eventually may rise on the surface on another place on the planet and create new crust. This is often referred to as recycling of the plates.