Which of these events occurred first?
a. the fall of the songhai empire
b. the fall of the mali empire
c. the introduction of islam into west africa
d. the entrance of portuguese explorers into african territory..

Let's find the dates:

A.the fall of the Songhai Empire  - this happened in 1591
B.the fall of the Mali Empire - this happened around 1600. From the first two options we see that the first happened earlier!

C.the introduction of Islam into West Africa
-this happened during the time of Mansa Musa, who was a ruler until 1337 - this is earlier than option a and thus our best option so far!

D.the entrance of Portuguese explorers into African territory.. - these started around 1420, so later than option c.

The correct answer is C!