Answer:
The answer is B
Step-by-step explanation:
For a long time, europeans were ill-equipped to travel to the interior of Africa (in fact, one could argue that they still are, as many areas of inner Africa are very inhospitable). It was much easier for a portuguese merchant to set a trading post on the coast and establish alliances with the locals who lived further inland.
Remember that a lot of Africa is/was jungle. In fact, from Senegal all the way south to Angola, Africa is basically covered in tropical rainforest (although in recent times much of that forest has been cut to pave way for cities and infraestructure), and where tropical forests do not dominante, deserts frequently take place (as it happens in Namibia and Mauritania).