Answer:
A. volcanic activity
Step-by-step explanation:
In a subduction zone, a noticeable increase in volcanic activity can be observed.
A subduction zone is a plate margin in which a denser lithospheric plate goes beneath a lighter one. One such example is illustrated between an oceanic plate which subducts beneath a continetal plate.
When a plate subducts, it goes deeper into the earth and reflux melting of the plate occurs. The melting point of nearby rocks is considerably lowered by dewatering of the subducting plate. The water causes reflux melting and magma forms. Appropriate conduits like fractures can carry the magma to the surface to initiate volcanic activities. This is the origin of volcanic activities within the continent or continental volcanism.