The questions below refer to the selection "The Tragedy of Julius Caesar, Act II." An attempt to warn Caesar of the conspiracy occurs in the form of a

message Portia sends with Lucius.

letter from Artemidorus.

confession from Brutus.

conversation with Cicero.

The second is definitely the right one. Teacher Artemidorous knew about Brutus' conspiracy and in order to warn Caesar he wrote a letter where he says "Caesar, beware of Brutus; take heed of Cassius". He mentioned that Brutus is not loyal at all and that he is going to get a profit from the accident that may happen with Caesar soon which his guards might not prevent.