What was a factor keeping europeans out of interior africa until the late 1800s?

Which of the following was a major outcome of european imperialism in africa after the industrial revolution? o a. the area around the suez canal experienced decades of military conflict o b. africans in the belgian congo suffered forced labor and oppression o c. the discovery of rich matural resources led to african economic prosperity. o d. europeans brought disease to central africa, killing thousands.