Contact between the two great landmasses, Australia and New Guinea was restricted to few small groups of Torres Strait Islanders interacting with a few small groups of Cape York Aborigines, just as it had once been between the Stone Age hunter gatherers of Australia and the Stone Age New Guinea farmers
A. just as it had once been between the Stone Age hunter gatherers of Australia and the Stone Age New Guinea farmers
-IMO ( it refers to the contact)
B. just like it once had been among the Stone Age hunter gatherers of Australia and the Stone Age New Guinea farmers
-Just Like is almost always wrong comparison
C. just as the Stone Age hunter gatherers of Australia and the Stone Age New Guinea farmers had once done
D. similar to what the Stone Age hunter gatherers of Australia and the Stone Age New Guinea farmers had done once
-Shifts the meaning of the intended sentence ( the farmers didn't force the situation to occur)
E. like what had been done by the Stone Age hunter gatherers of Australia and the Stone Age New Guinea farmers
-Like cannot be used to compare clauses.