Where does the name stratovolcano come from?

A stratovolcano is a type of steep volcano, of great height and conical shape originated by the superposition of multiple layers (strata - hence its name) of solidified lava and other volcanic materials, after successive eruptions.

This type of volcanoes are characterized by producing periodic volcanic explosions, where the emanated lava is viscous, therefore hardens before reaching far, due to cooling of the material.

a is the answer i believe.