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which item would it be most important to include in an essay about the history of the mail system?

a picture of a postal carrier making deliveries of mail
a sidebar on the history of the envelope
a story of a lost letter finally being delivered
a time line of the developments in modern mail service

A time line of the developments in modern mail service

Explanation:

It will give background information and tell you all the other kinds of important events that happened.

mark twain, real name samuel langhorne clemens, was an american writer, humorist, entrepreneur, publisher, and lecturer. among his novels are the adventures of tom sawyer and its sequel, the adventures of huckleberry finn, the latter often called "the great american novel". wikipedia