Reading skills among high school students in Gotham have been steadily declining, which can only be the result of

Premise: Reading skills among high school students in Gotham have been steadily declining,

Conclusion: This is as a result of overcrowding in the schools.

Option A - Incorrect:
This answer choice doesn't weaken the argument because the argument is concerned whether or not overcrowding in the schools in Gotham is responsible for the declination in Gotham high school students' reading skills, and not the comparison on the cost of education offered between Gotham and other cities.

Option B - Incorrect:
We are concerned about the steady declination in the reading skills, not lower reading scores. Reading skills can be decreased and still not low.

Option C - Incorrect:
This claim is not relevant because the argument is not concerned about the comparison of the teacher-to-student ratio between Gotham schools and other school systems.

Option D - Incorrect:
This answer choice does not agree with the premise of this passage. At such, it's definitely outside the scope of this passage.

Option E - Correct:
This answer choice gives a concrete explanation of why overcrowding is not the major factor responsible for the steady decline of reading skills among high school students in Gotham. Hence, this creates a crack in the argument that weakens it.