OG题求解

Roland hints that the unemployment rate is high since 90% people know someone is unemployed.

Sharon disagrees and claims it is normal for 90% people to know someone who is umemployed at a normal umemployment of 5%.

For necessary assumption questions, just use negation and see if that would cause the arugment to cumble.  If so, that answer choice is correct.  You do not need to worry why other choices are not assumptions other than that these wrong choices have no impact on the argument.

Let's negate B.
Unemployment is normally concentrated in geographically isolated segments of the population. If this is true, then certain area will have extremely high unemployment rate (let's say 10.5%) while other areas will have extremely low unemployment rate (let's say it is 0.5%). The national average for unemployment is still 5%. Then in the area with low unemployment, every 200 people will have one unemployed.  Then if one knows 50 people, it is likely that none of these 50 people are unemployed. Sharon's argument falls apart.