Read this excerpt from "Types of Volcanoes." Volcanoes are structures formed around openings (vents) in the ground where molten lava, ash, or gas escape from inside the Earth. We have all heard of lava, but not everyone knows how it forms. Deep inside the Earth, rock that melted long ago beneath the Earth’s crust forms magma, a very hot liquid that mixes with dissolved gases and crystals. How does the author show that he is writing for readers who are not experts on volcanoes? He uses terms such as "ash," "crystals," "molten," and "magma." He writes about differences between what happens to the ground and what happens under it. He uses terms such as vents and dissolved gases and crystals. He says that the readers have all heard of lava, but not everyone knows where it comes from.