The Electoral College of the U

The Electoral College of the U.S. Did you know that the President and the Vice President aren't elected by (1) popular vote in the U.S.? Essentially, every four years, it isn't the American people who elect the rulers of our nation. Instead, when a registered voter casts his or her vote for President and Vice President, he or she also votes for an unknown "elector", or voting member, who will cast a ballot in a separate election that ultimately will choose the president. Thus, by voting for a Democrat presidential candidate, for example, a voter is really voting for a member of the Electoral College who is expected--but not required--to vote along (2) party lines, too.
You might be thinking, "Then, why do we vote?" Historically, before the (3) advent of television and radio, the Electoral College was established to avoid unfairness. People who lived in bigger cities, where there tends to be a more concentrated, greater population, had more of an advantage of knowing about the candidates compared to those who lived in more rural, secluded areas.
The electors, which are chosen by popular vote, are divided up among each state and the District of Columbia. The amount of voting members in each state is equal to the number of members of Congress. In total, there are 538 electors: 435 representatives and 100 senators, plus the three (4) constituents from the District of Columbia.
In almost every state electors are selected on a "winner-take-all" basis. To be more precise, the candidate for elector that wins the most votes in a state becomes elector for that state. During an election, each elector is required to cast one vote for President and another vote for Vice President. The presidential candidate that receives the majority of electoral votes (270 out of 538) for the offices of President or Vice President is elected to that (5) office.
The word "office", bolded after the (5) in the fourth paragraph, is closest in meaning to

A) Service
B) Branch
C) Agency
D) Department