When native americans first encountered europeans, what led to the european diseases being so deadly?
a. the native americans had no tribal doctors or healers.
b. native americans had been struggling with basic survival.
c. centuries of continental isolation meant the native americans had no immunity.
d. the diet of most native americans lacked meat, so they had no consistent amounts of protein.
e. most europeans spread the diseases on purpose.

Option c.

Explanation:

When the Native Americans first came across the Europeans, the past American period of limited diseases terminated with the arrival of the Europeans.

This can be understood in a way that when the Europeans were not there in the past the population as compared to Europe was limited and as the Europeans came , these interactions and the population led to the spread of deadly diseases like that of syphilis which spread widely  as the Native Americans had not developed the immunity against such diseases due to continental isolation for quite a long period.  

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