the conquest of the Persian Empire by Alexander the Great and establishment of Roman power. B.
Reason being that after conquering Persia, Alexander and his men learend of the cult of Isis, a religion promising immortality and wealth. Alex and his men decided to follow that religion. That is the religion followed up until the establishment of roman power. The establishment of Roman power caused an unpleasant end to the Hellenistic Age. During the hellenistic age, there was a cult of the greek godess Isis. But the Romans only believed in Christianity, after it was spread by St. Paul and named the official religion of rome by constantine.
This is why the Hellenistic Age started with the conquest of Persia, and ended with the establishment of Rome.