Why is B incorrect?

@Shiyi-Zhang, Happy to help! In the stimulus, the author is saying that before the economic downturn, regulatory standards for loan-making by banks were tightened and that during the downturn, banks contributed to the decline by loaning less money. The author concludes from these premises that if standards are relaxed, banks will lend more money. The question says, "The argument assumes that..." This is a strengthen with a necessary premise question. We're looking for something that must be true in order for the argument to stand a chance and that, if false, wrecks the argument. In the stimulus, there is a big gap between the authors' premises and conclusion. We don't know for sure that because the regulations on banks came before the reduction in loans that the regulations caused the reduction in loans. The author is implying causation from a correlation. In doing so, the author is assuming that regulations are the sole cause of banks lending less. Let's take a look at the answers. You asked about (B). (B) says, "the imposition of the tighter regulatory standards was not a cause of the economic downturn" The problem with (B) is that it's confusing what the author is saying is causing what. The author's conclusion is that the increase in bank regulations caused the reduction in loans. The cause of the economic downtown is irrelevant for our considerations since the author's conclusion doesn't have to do with the economic downturn. As a result, we can get rid of this choice. (A) says, "the downturn did not cause a significant decrease in the total amount of money on deposit with banks which is the source of funds for banks to lend" (A)'s negation is the downturn did cause a significant decrease in the total amount of money on deposit with banks which is the source of funds for the banks to lend. If (A)'s negation were true, then the argument would fall apart because there's an alternative cause for the decrease in loans. Since (A) is eliminating an alternative cause for the reduction in loans, it is a necessary premise for the argument and is the correct answer choice. Does this make sense? Let us know if you have any more questions!

Why is this not a strengthen with sufficient premise question? It was my understanding that here the answer had to bridge the gap between the premise & conclusion.