@businessgoose I think nothing needs to happen in a strengthen question. Instead, we are just looking for the answer that increases the likelihood of the argument being true, even if it is only a miniscule amount. In this case, we have 4 answers that are all sorta random, and one answer that is relevant. In a strengthen question, you can usually do process of elimination to get the answer correct if nothing feels right immediately.

To answer your question,

Why would they need to rise in the surrounding areas, re (E)? Would it not be fine enough if they just stayed the same while Granville's declined? / Is it showing support regardless, because it's demonstrating that the other regions, the ones that didn't institute this new time change, didn't see theirs go down

the reason E strengthens, or provides the most support, for the editorial by removing the suspicion that the decline in car accidents was because of a confounding variable. For example, if it was true that car accidents all around Granville also declined because it was Earth day and people weren't driving for emissions purposes, or a war suddenly spiked oil prices and teenagers who drive to school couldn't afford gas anymore, then we'd have reason to be suspicious about the evidence provided by the argument.

You're right that the Car accidents could've just stayed the same and the decline in car accidents relative to surrounding areas without the policy would also strengthen the argument; however, answer choice E goes above and beyond and tells us that Granville had a decline in accidents despite an increase in the surrounding areas. This is supports our argument by confirming that the "overall number of car accidents involving teenage drivers in Granville" was because of this policy change and not because of Earth day or war.

Regarding your last question

What if all those car accidents in the surrounding regions rose at different times though, like increased evening accidents? #help

This is irrelevant and it is also why answer choice C is wrong. If you broke down the subject it is teenagers who drive to school in the mornings. So the group mentioned in answer choice C, which is teenagers who work at jobs during the day and presumably aren't going to school, are just not in the scope of the argument. Likewise, what happens in the evenings is irrelevant because the scope of the argument also only includes making a change between 8:00am and 8:30am.

In my timed read-through of this passage I had chosen E over B because of my misinterpreting of the grammar. I had found where it mentioned the 19th century and had eliminated it based on the word "until". In my mind this meant that this glass making technique existed before but not during the 19th century so it could not differ from today.

I also misinterpreted support for E through the same sentence. The passage reads "before the 19th century the only..." which to me was suggesting that the author believes that all glass that was made before the invention of the new technique had been subjected to these impurities. Medieval glass was made before the 19th century and thus this is how this glass came to be.

Not sure why this one specifically gave me trouble over the others. Based off the analytics I seem to be the only one who psyched myself out on this question.