Self-study
A common genetic mutation that lowers levels of the enzyme cathepsin C severely reduces a person's ability to ward off periodontitis, or gum disease. ███ ██████ ████████ █████████████ █████████ ████ ███████ ████████ █████ ███ █████████ ██████████ ██ ███ ██████ ███ ███████████ ███ ██████████ ████ ██ ███████ ███ ██████ ██ ██████ ███████ ████ ████ ████████ ██ ████ ██ ████ ██ █████████ ██████████████
Summary
The author concludes that gum disease will be permanently cured once researchers find a way to restore a certain enzyme’s levels to normal. This is because lowered levels of this enzyme are a cause of gum disease.
Notable Assumptions
The author assumes there are no other causes of gum disease. Researchers might fix this one cause, but what if gum disease can be the result of something else?
16.
Which one of the following ██ ██ ██████████ ██ █████ ███ ████████ ████████
a
Restoring cathepsin C ██ ██████ ██████ ██ ███ ████ ███ ██ █████████ ██████████████
The author thinks that restoring this enzyme to normal levels represents one way to cure gum disease, but there might be other cures as well. In other words, the existence of another cure for gum disease does not invalidate the author’s proposed cure.
b
Genetic mutation is ███ ████ █████ ██ ███████ ██████ ██ █████████ ██
The argument assumes that lowered cathepsin C is the only cause of gum disease, not that the genetic mutation is the only cause of lowered cathepsin C. There could be many causes of this lowered enzyme, but as long as researchers can consistently bring it back up to normal levels, then those other causes don’t matter.
c
Researchers will soon ███████ ██ ███████ █████ ██ █████████ █████████ █ ██ ██████ ███████
The conclusion is qualified by the statement, “Once [researchers restore the enzyme to normal levels].” It doesn’t matter if they actually accomplish this task—only that gum disease would be eliminated if they do.
d
Persons who do ███ ████ ███ ███████ ████████ ████ ██████ ██████ ██ █████████ █ ██ ███ ███ ███ ████████
If this answer choice instead said, “Persons who do not have lowered cathepsin C levels do not get gum disease,” it would be necessary. As it stands, however, the argument is fine if people develop gum disease without the genetic mutation. They could have lowered cathepsin C from some other source.
e
A person whose █████████ █ █████ ███ ████ ████████ ██ ██████ ████ ███ ██████ ████ ██████████████
This references one of the author’s assumptions—that the lowered enzyme is the only way to get gum disease. If people could get gum disease in other ways despite researchers fixing the lowered enzyme, then gum disease would not be successfully eliminated, and the conclusion would fall apart.