Yellowstone National Park has the three necessary ingredients for hydrothermal activity: molten material close to the surface, broken rock material close to the surface, and ________.
A) plentiful precipitation
B) relatively high altitude
C) much limestone
D) steep slopes
E) acidic groundwater
Question 2
The eruptions of Yellowstone's geysers as well as most of the others on Earth can be characterized as ________.
A) regular
B) irregular
C) containing only steam
D) becoming much more frequent over time
E) mysterious as to how they come to be