Deb: it's worrisome that 80% of the people in this country know at least one person who did not finish high school.
erik: but the average person has about one hundred different acquaintances, so, even if the normal high school dropout rate is only 10%, most people will probably know at least one dropout.

erik's argument relies on the assumption that

The dropout rate varies little from region to region across the country.

Explanation:

Erik gets to the conclusion that 80% of the people in this country knowing one person who did not finish high school it´s not surprising. To do so, Erik uses as evidence the idea that the average person has one hundred different acquaintances and the average dropout rate is 10%.

However, Erik's evidence is a conjecture. His assumption is that the conjecture that every average person has one hundred different acquaintances and that the dropout rate is 10% everywhere without considerable varations, is true.

a is your answer hope this ! : )

answer; never again fought on union soil;