It dried up.
North Africa used to be a fertile grassland, even swampy in some spots, 12,000 years ago. By 1000 BC (actually quite a while before) it had dried up into what is the the largest desert i the world: the Sahara.
The people in the Middle Ages were still highly connected to the church. Priests, and clergy ruled during that time, & what the church said was almost interpreted as law. In the Renaissance they took a step away from church, especially after the bubonic plague and started focusing more on humanism.
The answer to this would be B- Longitudinal Study.
Answer:
The calendar
Explanation:
The egyptians invented the calendar so that they could know when the Nile would flood. I know I' m very late on this but I just want to help :)