Please answer and fast its a test i will give 50 points if right

Which of the following was a key accomplishment of the people of songhai? a. they had a strong military and became the largest empire in west africa. b. they established a center of islamic scholarship. c. they worked with iron and prospered from the gold-salt trade. d. they dominated in the trade of ivory, enslaved people, and animal skins.

As of 2013, the world’s total population was about

Experiment to investigate effect of medication on levels of stress in males and females. dependant variable?