In the Late Spring and Summer of 1993,the Upper Mississippi

In the late spring and summer of 1993,the upper Mississippi River basin experienced record high floods.However,the floodwater mass did not significantly affect the lower Mississippi River basin because _______________.

A) the input from the Ohio River flow was low
B) there was a drought in Louisiana
C) the southern levees were built higher during the summer before the water got there
D) All of these choices are correct.
E) None of these choices are correct.