Aand b represent two plates interacting, what kind of plates are they?

The correct answer is - Plate A is continental and plate B is oceanic.

On this image we can see two plates moving towards each other. The plate marked with the letter A is a continental plate, while the plate marked with the letter B is an oceanic plate.

We can also see that the oceanic plate is subducting bellow the continental plate, and the reason for that is that the oceanic plate is lower, denser, and heavier, thus it sinks bellow. Also we can notice the volcanic mountain, which is a result of the subduction zone, because the high temperatures, pressures, and magma from the mantle layer are able to penetrate towards the surface, thus resulting in volcanic activity.