Why is this not correct?

[Philly]

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Yep, the answer on the test is adverb -- just as it should be.
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[Johnny]

The answer given by the site is A: Pretty here is used as an adjective.

I thought it was an adv. that's why I raised this question.

[MikeNewYork]

The answer given by the site is A: Pretty here is used as an adjective.

I thought it was an adv. that's why I raised this question.

Can you provide a link to that question? I'd like to see it.

[Philly]

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I believe the quiz in question is this one:
Adjectives and Adverbs with the same form (12):
http://www.usingenglish.com/quizzes/answers.php?id=387
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Sentence #10
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Johnny, it seems that you may have misread the answer on the quiz.
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[Tdol]

I checked the database and it showed adverb. I resaved the entry to make sure that it was working correctly. One thing it could have been was that Johnny took the test at the time we were moving from one server to another and it could have been something to do the move.