1. Which of the following causes physical erosion?
a. Rivers
b. Carbon Dioxide
c. Oxygen
d. Forest Fires
2. Which of these is still affecting North America geologically, although it ended 10,000 years ago?
a. An Earthquake
b. The Last Glaciation
c. A Major Subsidence
d. Chemical Erosion of the Grand Canyon
3. What caused the formation of the Grand Canyon?
a. Continental Drift
b. Subsidence
c. Physical Erosion
d. A Tsunami