“A medieval manuscript called L contains all eighteen extant tragedies …… ten called the “select plays,” are accompanied in L by ancient commentaries and also
appear in other medieval manuscripts” “ancient”---old or past--- infers that the commentary were arising from other extant manuscript, not written by the author of L. Ten of them, along with their commentary, must appear in at least one of other extant manuscripts.
Conclusion: If Electra does not have commentary in L, it must follow that all other extant manuscript do not contain any of its commentary.
C is incorrect “ no commentary is written about Electra in ancient time.” ancient time is too broad defined, medieval manuscript up to the point of L is only a small fraction of it. How do you know, no one after that time point has written any commentary about the play.