it describes a hypothetical situation.

A is the only one that uses 'were' which is correct usage in this sort of condition.

so A is the answer

"It looks as if its going to rain." vs "It looks as though its going to rain." - Both of these statements have the same meaning and it is a similar usage in the example given above in the question.

But the more grave error is the "were" usage which is compulsory no matter "as if vs as though " . First I'd make sure the were part is settled & correct before looking for other potential errors. Hope it helps!
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In this question we are lucky to have only one answer choice as were. Incase option c and e also had were instead of was, what would be the ideal answer in that scenario. Will it affect our choices, sorry if i am going off topic but couldn't help bringing it up

Posted from GMAT ToolKit
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This sentence is in subjunctive mood, since the imposter is not really a licensed practitioner, but is just trying to fake it. So it is a hypothetical scenario.
In case of subjunctive mood were is used instead of was. Just remember these famous lines from Tim Hardin's song

If I were a carpenter, and you were a lady
Would you marry me anyway?
Would you have my baby?

Now in this question only option A correctly portrays the subjunctive mood, but in case there were 2 options as below

-- as though she were a licensed practitioner
-- as if she were a licensed practitioner

Then it would have been tough to select the correct answer, as grammatically both are correct and imply the same meaning.
There is a very subtle difference between "as if" and "as though", "as if" is used to refer to a less likely scenario. For e.g.
1.) You are so scared of him as if he is going to eat you.
2.) You are so scared of him as though he is going to hit you.

Now you could also use "as if" in the 2nd sentence but given a choice "as though" would be more suitable.

Coming back to the original sentence, the imposter could have easily been a licensed practitioner, it's not like she behaved as if she were a dragon.
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