The correct answers are:
- New oceanic crust is created;
- Volcanoes erupt and produce more crust;
- Old crust is pushed away from ocean ridges;
When we have a divergent plate boundary, the plates move away from one another. As they move away, they leave a gap behind them, and lot of cracks in the thinner crust left behind. The high pressures from the mantle manage to push upwards the magma very easily through that crust and cracks. As the magma reaches the surface, it creates underwater volcanic activity. The magma comes out on the seafloor and quickly cools off. As it cools off, it creates new oceanic crust, thus the oceanic ridges. Because of the movement of the plates, and the constant new creation of new crust, the old crust is pushed away from the oceanic ridges.