Avolcano is best defined as
a. a dangerous geologic area
b. the site of a violent eruption
c. a chamber below-ground that is full of molten rock
d. a place where some magma reaches earth's surface

D. A place where molten magma reaches the earth's suface

Explanation: A volcano in line with option D is described as a vent or fissure on the surface of a planet (usually in a mountainous form) with a magma chamber attached to the mantle of a planet or moon (volcanoes do occur on other planetary bodies too) periodically erupting forth lava and volcanic gases and ash onto the surface. They are of three types: the strato or composite, the shield and dome based on their features and shapes.