The british often used a "mask" to keep their messages secret.
hidden within what looked like an ordinary letter
was the secret message that was only revealed when the
reader applied the mask. the writer might send the letter
by one rider going by one route while another rider carried the mask on another route. such letters had an
extra advantage: the writer could include false
information in case americans intercepted the letter.

which statement best states the central idea?

-a mask was a useful way to send messages.

-letter writers could travel via several routes.

-writers could include false information.

-a mask was needed to read a message.