I want to say B. The Columbia River. BUT a website says The Lake Missoula Flood is believed by some geologists to have carved out the Grand Coulee and Dry Falls in north central Washington.8 The Grand Coulee is a gorge about 80 km long and up to 300 m deep. Dry Falls sits at the head of a gorge about 100 m deep and 5 km long about midway in the Grand Coulee.
https://creation.com/only-one-lake-missoula-flood
Try to look it up on google.
