Final answer:
Philip of Macedonia and Alexander the Great transformed the ancient Greek city-states by conquering them, leading to unification under Macedonian rule and the start of the Hellenistic era. option D
Step-by-step explanation:
Philip of Macedonia and his son, Alexander the Great, most changed the ancient Greek city-states by conquering them and unifying them into one country.
This occurred after Philip's victory at the Battle of Chaeronea in 338 BCE, where he defeated the allied forces of Athens and Thebes, and subsequently worked to unite the Greek city-states under his leadership.
Shortly after, in 336 BCE, Philip was assassinated, and Alexander the Great adopted his father's plan and continued to enforce Macedonian hegemony over Greece, though later focusing on expanding their empire to the east by toppling the Persian Empire.
The control of Greece then passed from independent city-states to a united entity under Macedonian rule, leading to the establishment of the Hellenistic era, which marked a significant shift in Greek culture, economy, and political structure.
So option D is correct.