The subduction interaction occurs when an oceanic plate meets a continental plate and this pushes the oceanic plate underneath the continental plate.
The divergent interaction happens if two plates are moving apart, leaving a space where magma can be pushed up from the mantle, creating a new crust.
The transform interaction occurs when two plates slides past each other, cracking and breaking but not creating any new crusts.
In the image we can see that the interaction happens in an area where the land meets the water, and there is one plate (oceanic) going underneath the other (continental). Therefore, the correct answer is a) subduction.