Question: The Appalachian Mountains, which extend from Canada to Alabama, were much taller in the past than they are today. Which of the following two processes are most responsible for the decrease in the height of the Appalachian Mountains?

  Options: 
 A. weathering and erosion
 B. sedimentation and flooding
 C. volcanic eruptions and landslides
 D. tectonic collisions and earthquakes
Answer: A