B. Each is nominated by his or her respective party
Explanation:
Part of the reason parties exist is to endorse a single candidate by the time elections draw near. There are primaries in which democrats or republicans can each vote for which of the available candidates in their party they want to face the chosen candidate of the opposing party.
It created a large economy around the business of transportation and it made going around and transporting goods across the states easier witch helped the trade of goods.
