18. How do we know that a volcano is an active volcano?
A. It erupts regularly
B. It has a recent history of eruptions
C. If it shows activity like lava and ash flows or gas emissions
D. All of the above

19. What happens when volcano erupts? A. A scenic cone-shaped structure may be produced or changes on its slope can be observed.
B. The emissions of a volcano provide us with clues on what materials are found inside the Earth
C. Can spew hot, dangerous gases, ash, lava and rock that can cause disastrous loss of life and property
D. All of the above

20. Arrange the following to show how the heat from the Earth is tapped as a source of electricity in a power plant.
l. Heat from inside the Earth.
II. Steam causes the turbine to turn.
III. Heat causes the water to turn into steam. IV. Generator changes the mechanical energy to electrical energy.
A. I-III-II-IV
B. I-II-III-IV
C.JI-III-IV-l
D. I-IV-IH-l​