“Limited number of Natives available to fight back against the colonists” was the main benefit to the spread of disease in the New World for the colonists. This led to Natives being more easily overtaken by the colonists.
The correct answer between all the choices given is the first choice or letter A. I am hoping that this answer has satisfied your query and it will be able to help you in your endeavor, and if you would like, feel free to ask another question.