Why Would It Be Difficult for a Third Major Party

Why would it be difficult for a third major party to be successful?

A) The support for a third major party is spread across people of widely varying ideologies.
B) The support for a third major party is well below 50 percent.
C) The support for a third major party is concentrated among far-right conservatives.
D) The support for a third major party is concentrated among far-left communists.
E) The United States Constitution specifically states that there should be only two major parties.