At a convergent boundary, the correct description is:
D. collisions occur as lithosphere plates move toward each other.
At convergent boundaries, tectonic plates collide, which can lead to various geological features and events, such as the formation of mountains, deep ocean trenches, and volcanic activity. This collision can also cause earthquakes due to the stress and deformation of the Earth's crust. The other options describe different types of plate interactions: A refers to gravitational forces but doesn't accurately describe convergent boundaries, B describes transform boundaries where plates slide past each other, and C describes divergent boundaries where plates move apart.