The correct answers are:
- temperatures and terrain;
- human resources and natural resources;
The coastal part of West Africa has a tropical wet climate, and even though it is summer for all of the year, the temperatures are not extremely high. Also, there's lot of rainfall in this region. The terrain is mostly composed of lowlands. The Sahel on the other hand, is very dry, with extremely high temperatures, very little rainfall. Also, the terrain is ragged, with dry, steep, barren hillsides dominating the landscape.
West Africa has lot of human and natural resources. The region has relatively high population, especially young and middle aged population, and it is constantly growing. There's multiple natural resources as well, like oil, natural gas, gold, diamonds, water. The Sahel has very few people living in it, thus it lacks in human resources badly. The natural reserves are not abundant, nor there are many for exploitation.
