The feature that forms when one plate is forced to bend and dive under the other is typically a trench. However, based on the options provided, the most relevant response in the context of collision between plates, specifically an oceanic plate diving beneath a continental plate, would be:
a submarine volcano
This is because the subduction of the oceanic plate can lead to volcanic activity as the plate melts and magma rises to the surface, often resulting in volcanic cones. However, it’s important to note that the initial formation described (the trench) is a significant feature of subduction zones.