What Role Did Disease Play in European Colonization

What role did disease play in European colonization?

A) It decimated native populations leaving little resistance to European incursion.
B) It decimated European explorers and left them unable to face native armies.
C) It caused the spread of disease and mutation of new forms that were more dangerous.
D) It made colonization more difficult,as Europeans had to bring doctors with them.
E) It had a minor role in colonization,although there were losses among both Europeans and natives.