Take another look at the item:

You might think (A) that a floor-length dress is conservative (B) until you see the one that Christina wears. (C) A psychedelic swirl of pinks and purples that attracts everyone's attention.

You wanted to do this:

You might think, that a floor-length dress is conservative until you see the one that Christina wears. A psychedelic swirl of pinks and purples that attracts everyone's attention.

Adding a comma after think is an error. That a floor-length dress is conservative is a subordinate clause. When you connect a subordinate clause to the end of a main clause, you generally do not use any punctuation.

You might want to review the rules.

Go back to the sentence to try again.

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