Explanation:

A vent (opening) in the Earth's crust through which molten material erupts suddenly is called a volcano.

Volcano:
A volcano is a geological formation where molten rock, gases, and volcanic ash erupt through the Earth's surface. It is created when there is a rupture or crack in the Earth's crust, allowing magma from beneath the surface to rise and erupt. Volcanoes can be found on land or in the ocean and are typically cone-shaped mountains with a vent or crater at the top.

Crater:
A crater is a depression or hollow area at the top of a volcano. It is formed when a volcanic eruption causes the collapse of the volcano's summit or when an explosion blows out a portion of the volcano. Craters can vary in size and shape and are often surrounded by steep walls.

Earthquake:
An earthquake is a shaking or trembling of the Earth's surface caused by the sudden release of energy in the Earth's crust. It occurs when there is a sudden movement or shifting of tectonic plates along faults or fractures in the Earth's crust. Unlike a volcano, an earthquake does not involve the eruption of molten material.

Crust:
The Earth's crust is the outermost layer of the Earth's surface. It is a thin, solid shell that covers the entire planet. The crust is made up of various types of rocks and minerals and is divided into oceanic crust and continental crust. The crust is where volcanoes, earthquakes, and other geological phenomena occur.

Conclusion:
Therefore, the correct answer is option 'B' - volcano. A volcano is a vent (opening) in the Earth's crust through which molten material erupts suddenly.

It all depends on the region and the surrounding situation ,plus the fact of molten rocks who perform a cycle or process of colliding.