Take another look at the original sentence:

For two weeks, Todd refused to go to his accounting class because Professor Gastineau would not allow students to wear hats in class, under no circumstance would Todd allow anyone to see the butcher job his stylist had done to his hair.

You wanted to fix it this way:

For two weeks, Todd refused to go to his accounting class because Professor Gastineau would not allow students to wear hats in class, therefore under no circumstance would Todd allow anyone to see the butcher job his stylist had done to his hair.

Adding therefore will not fix the comma splice. Therefore is a conjunctive adverb and has no special power when you are joining two main clauses.

You might want to consult the rules for fixing comma splices and fused sentences.

Go back to the sentence to try again.

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