Actor: Bertolt Brecht's plays are not genuinely successful dramas.
Conclusion
BB's plays are not genuinely successful dramas.
Evidence
For a play to succeed, audiences must care what happens to at least some of the characters.
In BB's plays, audiences always find it difficult to discern any of the characters' personalities.
Evaluate
There's no new term in the Conclusion. BB's plays are described in the evidence, and there's a logical rule provided that allows us to conclude that a drama is unsuccessful.
The latter is more important, since that's our job on this problem:
audiences don't care what not successful what happens to any of → drama the characters
Our #1 job in the answer choices, then, is to establish that when it comes to BB's plays, audiences don't care about what happens to the characters.
The one detail we currently have, that an answer choice could build onto, is that when it comes to BB's plays, audiences find it difficult or impossible to discern any of the character's personalities.
Goal
The most likely answer would connect what we know about the audience reaction to BB's plays (can't discern personality), to the audience reaction that proves unsuccessful drama (don't care what happens to the characters).
So we'll look for
can't discern personality → don't care what of characters what happens
But we'll take any answer that would allow us to establish that when it comes to BB's plays, audiences don't care about what happens to the characters.