French explorers primarily focused their efforts on the Mississippi River and the St. Lawrence River. The Mississippi River was crucial for exploration and trade, with explorers such as Jacques Marquette and Louis Jolliet navigating it in the 17th century, while Samuel de Champlain explored the St. Lawrence River and established Quebec as a significant settlement.
The correct pair of rivers that were frequently the focus of French explorers is Mississippi and St. Lawrence. They explored both rivers for trade routes and to expand territories in North America.