What Was the Significance of American Telephone and Telegraph

What was the significance of American Telephone and Telegraph?

A) It was the first telephone company in the United States.
B) It was formed in order to boost competition between local phone companies.
C) For many years, AT&T was the only phone company in the United States.
D) It regulated the telephone industry to ensure no one company dominated the market.
E) It was the consolidation of many local phone systems into one large corporation.