You usually shouldn't care for where to use these sentences, but just as an example, imagine spies who are in an females-only college or something. A few of the spies get uncovered, but the rest remain among women. You really have to stretch your imagination for these kinds of phrases, so intead, just try to focus on learning the language.
Has anyone else experienced discrepancies between the error message and the given solution? I typed "entre femmes", and it dinged me for using the plural instead of the singular, but the correct solution also said "entre femmes".
I had also typed "Elle reste" instead of "Elles restent", but a) Duo usually accepts that, and b) it didn't mark that as incorrect.