As per the constitution, congress is able to exercise "commerce power" when it comes to
a. the taxing of exports.
c. favoring ports in one state over another.
b. regulating interstate and foreign trade
d. requiring duties.

loess contribute to the flooding of rivers by providing the silt that is washed into rivers and constantly raises the bed of the rivers. this elevation above the surrounding flood plains and dams allow the river to overwhelm the dams and flood thousand of square miles of neighboring flood plains.