In a group discussion, which sentence is most clearly challenging the credibility of a source?
a. piracy is a sensitive issue, and it's unfortunate that peterson's book about it has been republished recently.
b. peterson's goal was to tell a story, not argue a point, so his opinions aren't really that important.
c. although peterson's comments may have been valid at one time, his book is over 30 years old.
d. when peterson calls the ship the ransom, he's clearly making a reference to modern piracy.