Read the excerpt from Into the Unknown by Stewart Ross, and then look at the map below.

Her plan was to travel as far as she could up the great brown Ogooué River, which winds almost 700 miles into the heart of Gabon.

The Mové steamed south along the coast, crossed the equator in the afternoon, and reached the broad mouth of the Ogooué by evening. Chugging steadily upriver, over the next two days the steamer carried Kingsley between banks of overhanging forest to the small settlement of Lambaréné, 130 miles from the sea.

A geographical map of Gabon, showing bodies of water and mountain ranges.

How does the map help the reader understand the information in the excerpt?

A. It explains how far steamers could travel upriver.
B. It shows the Mové’s journey across the equator.
C. It gives visual details of the forests and river banks.
D. It shows the location and the size of the Ogooué River.