The 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 use of the comma before "and so" can be considered optional or contested depending on style guides.
-
Faith, Millie's best friend from summer camp, is coming to visit in a few weeks.
- The use of the commas around the appositive "Millie's best friend from summer camp" can also be viewed as contested, particularly if the appositive is a more complex phrase. Some might argue that it can be omitted in certain contexts.
(Note: Both of these usages can vary in acceptability depending on the guide one follows and the structure of the sentences.)