Answer: D. Crust
An volcanic eruption is a natural expulsion of gases, hot lava, dust and rocks from the undersurface of earth. The released lava gets cool and solidifies into a layers of crust. A volcanic eruption is the earth's way of renewing itself. A volcano can be active, dormant or in extinct state. An active volcano involves an erupting lava, gas and shows seismic activity. A dormant volcano is the one that has not erupted for quite a long time but can erupt in future. A extinct volcano is the one that has been dormant or static for long time and has not shown any sign of activity.