-- If A burns out, then all six bulbs go out, and an inky blackness descends over the whole circuit. (Choice-A). The battery is happy though, because it doesn't have to supply ANY energy.
-- If D or E burns out, then all five of the not-burned-out bulbs still shine.
-- If F or C burns out, then A, B, D, and E still shine.
-- If B burns out, then A and D still shine.