In the test question: ¿Quién es ________ de tus amigos? (Who is the most generous of your friends?)
I incorrectly assumed that because "de tus amigos" doesn't specify the gender of "Quien es" in Spanish, that "lo" would be appropriate rather than "el" (correct answer). Because only the response can reveal the gender e.g. - "Carla es la más generosa de mis amigos" o "Jorge es el más generoso de mis amigos". In other words, why is "el" correct in this case even if the "quién es" might turn out to be female? (I did notice that the hint was "generous = generoso" but (falsely?) assumed it was being generic rather than specifying un amigo masculino).
Can you please clarify?