Question

The Sahara served as a(n) _____________, ______________ the rest of the world.

A. oasis/uniting Africa with
B. barrier/isolating Africa from
C. avenue for trade/connecting Africa with
D. means for isolation/barricading Africa from

Answer 1

Sahara is a desert and deserts are hard to cross. Sahara is especially bad and potentially deadly: it's very dry and there is no water to be found for miles.

Therefore it was a barrier and it has isolated South Africa from European influence for a long time. (until the time of European explorations)