Which body of water separates the Upper and Lower Peninsulas?

The Straits of Mackinac is the correct answer because it is the narrow waterway that directly separates Michigan's Upper Peninsula from its Lower Peninsula. This strait connects Lake Michigan to Lake Huron and serves as a significant geographical feature for understanding how the two peninsulas are divided. The Straits of Mackinac also plays a crucial role in transportation and regional ecology.

In contrast, the Great Lakes are a larger group of freshwater lakes that include Lakes Superior, Michigan, Huron, Erie, and Ontario; while they encompass both peninsulas, they do not specifically delineate their separation. The Detroit River and Saginaw Bay are other bodies of water in Michigan, but they are not located between the Upper and Lower Peninsulas. The Detroit River forms a boundary between Michigan and Canada, specifically separating the state from Ontario, while Saginaw Bay is an inlet of Lake Huron located on the eastern side of the Lower Peninsula.