The two sentences that use a comma in a way that is considered contested usage are:
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Stephen did not understand the question, and so Gina tried to explain it to him more clearly. - The use of the comma before "and so" is contested. Some people argue that a comma should not precede "and so" in this context.
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We are passing through New Orleans, Louisiana right before we stop in Houston, Texas. - The comma usage before "Louisiana" and "Texas" can also be seen as contested. Some writers prefer to use an additional comma after "Louisiana" and "Texas" for clarity, as in "We are passing through New Orleans, Louisiana, right before we stop in Houston, Texas."