What is the name of the longest river in the world, running northward through northeastern Africa?

The question asks for the name of the longest river in the world that runs northward through northeastern Africa.

• A. The Yangtze River is in Asia and flows eastward.
• B. The Nile River is located in northeastern Africa, flows northward, and is traditionally considered the longest river in the world. This matches all the criteria in the question.
• C. The Amazon River is in South America and flows eastward.
• D. The Mississippi River is in North America and flows southward.

Based on the description, the correct answer is the Nile River.

$\boxed{B. Nile River}$