Answer:
A. explain the use of invisible ink during the American Revolution.
Step-by-step explanation:
The author's main purpose in this excerpt is to explain the use of invisible ink during the American Revolution. The author describes two types of invisible ink used by British agents and how they could be made visible. The author also mentions Major John Andre, the chief British intelligence officer in New York, and his instructions to agents regarding the use of these inks. All of this information is presented in the context of the American Revolution, indicating that the main purpose of the excerpt is to explain the use of invisible ink during this historical period.