What part makes up part of the southern boarder of the northwest territorie

A. Ohio river

Explanation:

The Northwest Territory, also known as the Old Northwest and formally known as the Territory Northwest of the Ohio river, was formed in the United States after the American Revolutionary War. Established in 1787 by the Congress of the Confederation through the Northwest Ordinance, it was the nation's first post-colonial organized incorporated territory.

the real answer is b

is there answer chooses?