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. The enzyme triggers immunological reactions that destroy diseased cells and eliminate infections in the mouth. But researchers are developing ways to restore the enzyme to normal levels. Once that happens, we will be able to eliminate periodontitis.
Which one of the following is an assumption on which the argument depends?
(A) Restoring cathepsin C to normal levels is the only way to eliminate periodontitis.
(B) Genetic mutation is the only cause of lowered levels of cathepsin C.
(C) Researchers will soon succeed in finding means of restoring cathepsin C to normal levels.
(D) Persons who do not have the genetic mutation that lowers levels of cathepsin C do not get gum disease.
(E) A person whose cathepsin C level has been restored to normal will not suffer from periodontitis.

(E) A person whose cathepsin C level has been restored to normal will not suffer from periodontitis.

Explanation:

Considering the fact that there may be some other causes of periodontitis aside from the lowered levels of the enzyme.

Therefore, should there be some other causes of periodontitis, hence, it can be concluded the process of restoring the enzyme to normal levels might not be sufficient for eliminating periodontitis.

Hence, the author's argument is solely based on this assumption, and option. Hence, option (E) is the correct answer.

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