Final answer:
In 'Antigone', the protagonist invokes the concept of family duty to justify her intentions to bury her brother against the king's orders. The word that best fills in the blank in the student's question is 'duty'.
Step-by-step explanation:
In Sophocles' tragedy Antigone, the main character, Antigone, reminds her sister Ismene of their family duty when she tries to persuade her to help bury their brother Polyneices, despite the king's edict against it. Antigone appeals to the higher laws of the gods and familial responsibilities over the worldly laws enacted by Creon, demonstrating her strong belief in what she perceives as a sacred obligation to her family, particularly in honoring the dead. The correct answer to fill in the blank would, therefore, be D. duty.