Reading skills among high school students in Gotham have been steadily declining, which can only be the result of overcrowding in the schools
This means that there are no reasons other than overcrowding
which can explain the reading skills decline.
Something which will weaken the argument will cast some doubt and open the possibility to some reasons other than overcrowding.
A) this could actually strengthen the argument because if costs are less, we could blame this on overcrowding of classes resulting from budget costs.
B) this has the argument backward and cannot be ascerted. For all we know, we are trying to disprove the opposite: that reading skills are affected by overcrowding
C) yes, they may have a greater T/S ratio but what if those other schools have really lower T/S ratios already
? Overcrowding could still be the cause of Gotham's low reading skills
D) we're not interested in schools where the reading skills have not declined
. Rather, we are interested in instances where reading skills have declined and find if overcrowding is the direct and only cause.
E) eureka. We have an instance in which reading skills have declined but yet, there is no overcrowding. This confirms that there must be some reason other than overcrowding
which lowers the reading skills of students in Gotham