Carlos is looking at a picture of a convergent boundary on which a volcanic arc and a trench are identified. which type of convergent boundary is carlos looking at?

The answer would be:

Oceanic-Oceanic Convergent Plate

This is why:

When two oceanic plates collide, the heavier of the two would subduct or in other words, go under the other plate. When this happens, ocean trenches and volcanic arcs form. The trench forms at the point oceanic plate goes under the other plate. And above the other plate that goes over create volcanic arcs.  

the answer is c.the valence of the atoms combine .