Which of the following markets is an example of an oligopoly?

When Ben Bernanke referred to the exit strategy of the Fed, he was referring to:

A) his plans to retire as chair of the Fed B) when the Fed would stop implementing monetary policy C) the process by which the Fed would shrink its balance sheet D) increasing the federal funds rate back to where it was prior to the financial crisis

Even if a firm is optimistic about the future, why should it shut down if it cannot cover its variable cost? If it does shut down, are there ramifications not mentioned in the textbook?