Answer:
main vent - this is the channel through which magma travels to reach the Earth's surface. secondary vent - some magma may escape through the side of the volcano, particularly if the main vent becomes blocked. crater - this is found at the top of the volcano, where the magma erupts from.
I think it is C, since it sounds the most reasonable.
A. Because the call isn’t urgent and he politely acknowledged the call, but asked if he can call back later since it isn’t urgent