Which sentence uses brackets correctly?
a) since the speaker is going mad, I wonder if it [the raven] is actually perched above the door
b) since the speaker is going mad, I wonder if [it the raven] is actually perched above the door
c)[since the speaker is going mad], I wonder if it the raven is actually perched above the door
d) since the speaker is going mad, [I wonder if] it the raven is actually perched above the door