native peoples of america had no immunity to the diseases that european explorers and colonists brought with them. diseases such as smallpox, influenza, measles, and even chicken pox proved deadly to american indians. europeans were used to these diseases, but indian people had no resistance to them.
the answer is b) individual - this is referencing ones rights to the pursuit of happiness, or basic human rights for an individual.
i don't know why don't you google it?