Steep sided cone or composite volcano would most likely be found at

a) an oceanic hot-spot.
b) a subduction boundary.
c) a rift (divergent) boundary.
d) a continental hot-spot.

b) a subduction boundary

Explanation:

The subduction boundaries, or convergent plate boundaries, are the places where the tectonic plates are colliding, and one of them subducts below the other. As one of the plates moves below the other, there's lot of pressure, and cracking occurring in the crust, so the magma manages to penetrate through it and comes out on the surface with ease. As it manages to get on the surface, it lifts up the land, and creates a cone shaped volcano. This volcanoes manage to make a very nice shape, the stereotypical volcano shape, and that is a result of constant pilling of material on the slopes of it. Some of the volcanoes that are regarded as the most beautiful are actually volcanoes of this type, like Mount Fuji in Japan for example.