History help, which man is greater?
The point of this question is not for you to pick the “right one” (unless your teacher is a complete tool). There is no way of definitively saying who was the “greatest” whatever that means. It is testing your powers of argument. Just pick one, do your research and make the case pointing out why he was more significant than the other three. You could. for example, argue that Napoleon had greater lasting impact on European civilisation the way he ruled France. You could say that Marx was more influential because of the global impact of communism (but did it last like Napoleon’s structures?) in his name. You could say Bismarck’s united Europe’s most potentially powerful country and his legacy lead to two world wars and you could argue that Garibaldi’s task of unification in Italy was more difficult plus he helped Uruguay to gain independence.
