Read the text carefully and answer the following question! A volcano is a rupture in the crust of the earth that allows hot lava, volcanic ash and gases to escape from a magma chamber below the surface. A volcano mountain is formed by the eruption of material from the earth’s interior through a central opening or groups of opening. Volcanoes can be divided into three categories based on volcano form and type of volcanic activity. They are shield, composite, and explosion volcanoes. A shields volcano is built chiefly of layers of basalt (a dark and heavy lava). A few shield volcanoes are composed of andesite (a related, less dense type of lava). A composite volcano has more frequent and violent explosive eruptions than shield volcanoes do. Lava may be extruded from either crater or fissures on a volcano’s sides. What is the main idea of text above?

Question

Read the text carefully and answer the following question!

   A volcano is a rupture in the crust of the earth that allows hot lava, volcanic ash and gases to escape from a magma chamber below the surface.
   A volcano mountain is formed by the eruption of material from the earth’s interior through a central opening or groups of opening. Volcanoes can be divided into three categories based on volcano form and type of volcanic activity. They are shield, composite, and explosion volcanoes.
   A shields volcano is built chiefly of layers of basalt (a dark and heavy lava). A few shield volcanoes are composed of andesite (a related, less dense type of lava).
   A composite volcano has more frequent and violent explosive eruptions than shield volcanoes do. Lava may be extruded from either crater or fissures on a volcano’s sides.

What is the main idea of text above?