Which nickname had the Senate earned by the end of the nineteenth century?

• A. Millionaires'
• B. BMOC
• C. Recalcitrant
• D. Vice President's

Answer: (A)

The main idea is that, by the end of the nineteenth century, the Senate was seen as dominated by wealth, earning it the nickname "the Millionaires' Club." During the Gilded Age, many Senators came from moneyed backgrounds—railroad barons, financiers, and successful businessmen—so money and political influence were tightly linked in public perception. This led observers to describe the Senate as a body of millionaires who wielded outsized power in politics.

The other terms don’t fit this context. BMOC is college slang for the "Big Man on Campus," not a historical label for a national legislative body. Recalcitrant means stubborn or resistant, which is not a nickname for the Senate. "Vice President's" would be ambiguous and does not capture the sense of wealth and influence that the nickname conveys.