The numbers that Major Tallmadge assigned to members of the Culper Ring were from a secret writing system he invented. He substituted digits for words that would be used in messages. "Long Island," for example, was 728, "arms" was 7, and "city" was 88. There was a number for each month, such as 34l for "January." He made four copies of his codes. He kept one and gave the others to Woodhull, Townsend, and General Washington. For words that did not have a number code, Tallmadge gave his agents a cipher. In a cipher, each letter in a message is replaced by another letter or a number. Which best describes the central idea of this excerpt?

Major Tallmadge created a code that substituted numbers for words during the Revolutionary War.
Major Tallmadge created a code in which “city” was “88” during the Revolutionary War.
During the Revolutionary War, Major Tallmadge gave General Washington the key to his codes.
During the Revolutionary War, Major Tallmadge gave soldiers a cipher for words not included in the code.