Take another look at the sentence:

Jean always nibbles around the pit of a cherry, just as if she were eating a peach, because she is vain about her smile, she doesn't want to chip a tooth on the hard center.

The comma between smile and she is completely correct. Because she is vain about her smile is a subordinate clause. A subordinate clause cannot stand alone as a complete sentence. You must attach it to a main clause to finish the thought. She doesn't want to chip a tooth is the main clause that completes the idea.

Go back to the sentence to try again.

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