After reading this passage:
Shakespeare used an ancient biography, by the Greek writer Plutarch, as a source for the play Julius Caesar.
excerpt from Julius Caesar by William Shakespeare
Caesar:
Who is it in the press that calls on me?
I hear a tongue shriller than all the music
Cry "Caesar!" Speak, Caesar is turn'd to hear.
Soothsayer:
Beware the ides of March.
Caesar:
What man is that?
Brutus:
A soothsayer bids you beware the ides of March.
excerpt from Lives by Plutarch
Furthermore, there was a certain Soothsayer, that had given Caesar warning long before, to take heed of the day of the Ides of March (which is the fifteenth of the month), for on that day he should be in great danger. That day being come, Caesar going unto the Senate-house, and speaking merrily to the soothsayer, told him, "The Ides of March be come." "So they be," softly answered the soothsayer, "but yet are they not past."
The statement that best explains how Shakespeare drew from his source to help create the play is:
Shakespeare followed the source closely but changed its basic meaning.