Answer: d. mountain
Step-by-step explanation:
When two continental plates collide, the boundary (subduction zone) is destroyed and rocks will start to pile up as the collision continues.
This will lead to the formation of mountains and mountain ranges which will also join the plates together. The Himalaya mountains for instance were formed when the Indian plate collided with that of Asia and as they are still colliding today, the Himalayas are still rising.