Does a necessary assumption not “strengthen” an argument by eliminating one possible way the argument could be made invalid?

Could a NA be the answer to a strengthen question? #help

One of the better RC answer explanations I’ve seen. Good job, JY!

Each wrong answer choice contains a specific logical trap to tempt the test taker while inaccurately applying the artistic definitions in the stimulus. Some come close but miss a key detail in the stimulus. C is correct.