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 do not require a comma in such a case.)
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"We are passing through New Orleans, Louisiana right before we stop in Houston, Texas." (While the comma after "New Orleans" is generally accepted to set off the state, some argue about whether a comma should precede "right before.")
These usages can be seen as contested depending on the specific style guide or preference.