What body of water was important to both Mali and Songhai?

The Niger River was important to both Mali and Songhai.

The correct answer is the Niger River.

To determine the body of water that was important to both Mali and Songhai, we need to look at the options given. The options are: Senegal River, Atlantic Ocean, Niger River, and Tropic of Cancer.

Based on historical context, both the Mali Empire and the Songhai Empire were located in West Africa. One of the significant geographical features in that region is the Niger River. The Niger River is one of the longest rivers in Africa and played a crucial role in the economic and cultural development of both empires.

Therefore, the correct answer is Niger River.