Answer to Question 1
Answer: A
Answer to Question 2
Answer: When necessary, computer models replace field observations and experiments to test hypotheses. Computer programs describe the natural processes by mathematical equations and set the values for material properties and rates of processes that are difficult or impossible to control in the laboratory. However, even computer simulations have limitations, not only because of uncertainties in values for deep-Earth materials and processes, but also because they require immense computing power to simulate what happens within the huge volume of Earth during long periods of geologic time.