The 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" can be debated, as some style guides recommend omitting it in this context.
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We are passing through New Orleans, Louisiana right before we stop in Houston, Texas. - The use of the comma before "Louisiana" is generally correct, but the lack of a comma before "Texas" can be considered contested, as some styles may call for a comma in both instances when listing.
These sentences are often discussed due to differing opinions on their comma usage.