What Finally Convinced Sparta to Send Athens an Ultimatum Demanding

What finally convinced Sparta to send Athens an ultimatum demanding that it curtail its aggressive foreign policy?

A) Corinth, a Spartan ally, threatened to ally itself with Athens if Sparta did not intervene on its behalf to prevent future Athenian aggression.
B) Sparta feared that Athenian aggression abroad might antagonize the Persians into a renewed attack on the Greek mainland.
C) The Athenian general Alcibiades persuaded Corinth to break with Sparta and join Athens.
D) Corinth, an Athenian ally, attacked Megara, a Spartan ally, thus violating the terms of the Athenian-Spartan peace treaty.