Read the excerpt from "Tools of the Spymaster." Washington, a spymaster with a sharp eye for details, gave exact instructions on how an agent should use invisible ink: "[H]e should occasionally write his
information on the blank leaves of a pamphlet... a common pocket book, or on the blank leaves at each end of registers, almanacs, or any new publication or
book of small value." He also told his agents that a "much better way" is to write a letter "with some mixture of family matters" and the secret message, which
would be invisible, "between the lines and on the remaining part of the sheet."
What is the author's main purpose in the excerpt?
O A. to inform readers about George Washington's stealth and creativity
O B. to persuade readers that spying during wartime is heroic
O C. to teach readers about the dangers of being a spy
O D. to compare various methods of writing secret messages