Final answer:
Marc Antony gets into relationship with Cleopatra following Julius Caesar's assassination, which led to a significant political alliance and subsequently a civil war with Octavian (option b).
Step-by-step explanation:
After Julius Caesar was assassinated, it was Marc Antony who entered into both a political and romantic relationship with Cleopatra. Marc Antony and Cleopatra's relationship was an important alliance as it allowed them to rule the eastern provinces of the Roman Republic. However, this alliance eventually led to a civil war against Octavian, and following their defeat at the Battle of Actium and subsequent self harming behaviors, Octavian became the sole ruler of the Roman world.
Hence, the answer is option b.