The Mississippi watershed is the largest in North America, draining all or part of thirty-two states in the United States and two Canadian provinces. A new apartment complex is being built on a steep slope near the source of the Mississippi River outside of Minneapolis, Minnesota. Which of the following measures should be taken to best reduce erosion at the construction site to protect the Mississippi watershed?
a. Add a paved surface at the top of the slope.
b. Remove trees and shrubs from the slope and the riverbank.
c. Move all of the topsoils from the site to the riverbank.
d. Plant grass and shrubs on the slope.