Final answer:
The Battle of Thermopylae was a heroic stand by the Spartans against the Persians, and the missing word in the student's question is likely intended to be 'heroic' option c is correct.
Step-by-step explanation:
The Battle of Thermopylae, which took place in 480 BCE between the ancient Greeks and Persians, was indeed a crucial event, but not as a 'turning point in the rise of the Persian Empire'. The battle represented a heroic last stand of a small Greek force, mostly composed of Spartans under King Leonidas, against the massive invading Persian army led by King Xerxes. The Spartans' objective was to delay the Persians to allow other Greek forces to prepare defences. Despite their eventual defeat due to betrayal and subsequent encirclement, the Spartans' resistance provided time for the Athenians to prepare their navy, which later defeated the Persian fleet at the Battle of Salamis.
The missing word in the student's question (1) is likely intended to be 'heroic' (C), reflecting the valor of the Spartans during the battle. Though the Spartans (and their Greek allies) eventually fell, their actions were celebrated for their courage and self-sacrifice, which inspired the greater Greek resistance against the Persians and eventually contributed to the Persians deciding to abandon their conquest of Greece after repeated defeats.