The only possible answer to this in the options given to us here is B. Theodore Roosevelt was known as the "Trustbuster." None of the other options is possible.
A and B cannot both be right. "Trustbusting" is the process of breaking up large businesses that hold monopoly power over a market. This is very much the opposite of fighting to protect big businesses. Roosevelt was known as the first president to aggressively use antitrust laws to go after big companies that, he thought, were harmful to the US economy and society.
I'm sure that answer B, earned the nickname Trustbuster, must be the standard answer to the question, but if you want to rattle your teacher's cage, consider the following.
Consider who benefits from Trust Busting. Consumers come to mind. Because of increased competition due to more companies competing in the market, the consumer benefits due to more choices and lower price. At least that is the theory.
But the stockholders, some of who would be millionaires, would also benefit because to compete in the market, each company would become more efficient, drop past bread winners, and find new breadwinners.
Companies, which depend on their monopoly position to return a profit, are not necessarily safe investments. For example the Cordage Trust went bankrupt.
The bankruptcy caused a financial panic.
So, trust busting could be a good thing for everybody, millionaires and big business included.
yes, "B"..."Trust Buster."