As is known to us all, the Sahara Desert is a natural _________ between north and central Africa．

1. A.
   barrier
2. B.
   routine
3. C.
   garment
4. D.
   basis

As is known to us all, the Sahara Desert is a natural______between north and central Africa．

A．barrier           B．routine        C．garment          D．basis

As is known to us all, the Sahara Desert is a natural           between north and central Africa.

A.barrier                 B.routine               C.garment                    D.basis