What Caused the Catastrophic 1997 Flood Along the Red River

Multiple Choice

What caused the catastrophic 1997 flood along the Red River in North Dakota?

A) thawing to the south of the frozen north-flowing river that backed up water behind the ice to the north
B) thawing of a heavy snowpack on the nearly horizontal surface of ice-age Lake Agassiz
C) heavy rains on a deep snowpack on nearly flat ground
D) a stalled warm front that was unusually far north for that time of year
E) a cold front from the north that intersected a warm front in the northern Mississippi valley