What Occurs When a Territory-Holding Male Zebra Finch Hears the Song

What occurs when a territory-holding male zebra finch hears the song of the male zebra finch that has held the neighbouring territory for a long time?

A) The territory-holding male initiates a ritualized threat display that may culminate in an expansion of his territory into the neighbour's land.
B) Cells in the nucleus of the territory-holding male zebra finch's forebrain fire frequently.
C) Cells in the nucleus of the territory-holding male zebra finch's forebrain do not respond to the song of the neighbouring male.
D) The territory-holding male flies out to drive off the neighbouring male.