PT131 · S3 · Q16 A common genetic mutation

The author is assuming that this is one way to eliminate periodontitis, but there's no way to support the idea that the author thinks it is the only way. In other wording, she does assume this method is Sufficient. She doesn't assume it's Necessary.

Too Strong: "only cause of low cathepsin C" It wouldn't trouble this author's argument if there were other sources of low cathepsin C, because the solution the researchers devise could presumably also help restore their enzyme to normal levels too.

There's no timeline on the conclusion / argument. It's just "once we get a solution, then periodontitis will be gone". The author never promises or insinuates that we'll get there soon.

Too Strong: "nobody else gets gum disease" This is pretty tempting, similar to how choice (B) is. When you negate them, they definitely raise doubt about the conclusion. For (B), if there are other ways to get low cathepsin C, then maybe those people would still get gum disease (because maybe the solution researchers devise for mutation-caused low cathepsin C wouldn't work for them). For (D), if there are people without the mutation that do get gum disease, then maybe they would still have gum disease, even in a world where we could restore your cathepsin C levels to normal. However, negating this answer certainly doesn't weaken as much as negating choice (E). With (D), it's possible that people who don't have the mutation but do get gum disease are still getting gum disease from low cathepsin C (something other than genetic mutation causes them to have low cathepsin C). In that case, the solution the researchers devise should be able to help these non-mutation people as well. If this answer were re-written as, "Persons who do not have lower levels of cathepsin C do not get gum disease", it would be correct.