What action does the author of "the great mississippi river" call on readers to take in the final paragraph?
a. "through navigation, commerce, and recreation, the river plays a central role in the lives of millions of americans."
b. "americans will have to learn how to address and support the ecological needs of this great watershed."
c. "this would provide guidance to farmers along the mississippi and other u.s. waterways."
d. "the mississippi river has long been crucial to the development and continuance of the u.s. economy and way of life."?