Here's why:

* Divergent boundaries are where tectonic plates move apart. This separation creates space, which is filled by magma rising from the Earth's mantle. As the magma cools and solidifies, it forms new crust, creating a mid-ocean ridge.

Let's look at the other options:

* Convergent boundaries are where tectonic plates collide. This can lead to mountains, volcanoes, and earthquakes.

* Transform boundaries are where tectonic plates slide past each other horizontally. This can cause earthquakes.

Therefore, the correct answer is divergent boundary.