Which line of longitude forms the dividing line between the great plains and the rocky mountains

100th meridian is the correct answer.

Explanation:

The hundredth meridian was drawn by American geologist and explorer John Wesley Powell and was meant as the boundary line between the arid west plains and humid eastern united states. It passes through Texas, Mexico, Oklahoma, Nebraska, Kansas, Dakotas and the Canadian province of Manitoba. Powell is famous for his exploration of Grand Canyon and Western plains.  He was aware of the harsh conditions of the region and tried to convince the congress to lay out water and land management districts  to deal with environmental constraints.

ok so u have2 basically

i am sure the answer is d