The two sentences that use a comma in a way that is considered contested usage are:
-
Stephen did not understand the question, and so Gina tried to explain it to him more clearly.
- The comma before "and so" is often considered optional; some style guides suggest that it may not be necessary.
-
We are passing through New Orleans, Louisiana right before we stop in Houston, Texas.
- The comma after "Louisiana" is often debated as it separates a city from its state. Many style guides recommend using a comma before the state name, but some may choose to omit it for brevity or clarity.
The other sentences use commas that are generally accepted according to standard punctuation rules.