@ConnerKline This also had my head spinning for a while so I hope my explanation can be helpful:

1981 to 1985 definition of serious accidents: more strict

after 1986 definition of serious accidents: less strict

Thus, based on this alone we would have expected to see the count of serious accidents go up in 1986 rather than go down. However, in reality what we actually saw was that the count of serious accidents did go down, despite the now less strict definition of serious accidents. This means that the smaller number of serious accidents is indeed smaller in 1986 than in previous years. In other words, if we kept the same more strict definition of serious accidents from 1985, then we may expect to see an even greater decrease in the number of serious accidents. If anything, the numbers from 1986 are inflated, compared to 1985. This does not weaken the argument that the speed limit led to a decrease in serious accidents.

just btw for anyone who is confused, kevin's explanation is a lot more helpful than JY's.

I read AC A as supporting the reasoning i.e.

variable climate -> hard to rule and defend -> hurt food production -> Rome fell

So answer choice A strengthening that 2nd part of the chain. Can anyone explain why this is not a valid way to interpret AC A?

It literally says that "some community members who favored Western notions of standard language writing or whose training in Western-style linguistics was especially rigid," implying that there is some Western-style linguistics used to make traditional language written. Thus, how can the answer be C?

Why can't we just think of All statements the same as conditional statements? Is the negation rule for both also essentially saying the same thing?

For the option 3 where "or" actually means "and", does that mean "Jane is a faster eater than either Mary or Jon" = "Jane is a faster eater than Mary and John"?

But "Jane is a faster eater than either Mary or Jon" /= "Jane is a faster eater than Mary or Jon"? ... where this now becomes option 2 usage of "or"?