What invisible enemy attacked the athenians in 429 bc?

The invisible enemy was the Plague of Athens, an epidemic that possibly reached from Africa to the city of Athens, during the Peloponnesian War, at a time when the Greeks could still win the war. Experts think that the plague, often identified as Bubonic Plague (although in recent studies it is thought that it was a hemorrhagic fever, or perhaps Typhus) entered the city-state of Athens through the port of Piraeus, its only source of food and supplies. Due to the lack of hygiene at that time, Athens became a propitious place of the palga, killing many Greeks, even General Pericles, who was a great Greek statesman, passed away after the death of his wife and children Xanthippus and Paralus. The plague of Athens finally decided the course of the Peloponnesian War.

The correct answer is b