This explorer sailed in parts of Florida and the Mississippi River in 1539. Who was he?

The correct answer is B. Hernando de Soto.

Hernando de Soto was a Spanish explorer who embarked on expeditions in the early 16th century. In 1539, he explored parts of Florida and traveled inland along the Mississippi River, making significant contributions to the European understanding of the geography of the southeastern United States. His journeys were important for mapping the region and expanding Spanish claims in North America.