"Boy, it is a shark!"
The "correct" answer "Ragazzo" makes it sound as if one is addressing a boy. But one would never speak to a child that way in English. It is too harsh and impersonal a command (with the exclamation point). It is the way Blacks were spoken to by racists in the U.S. even in the 20th century. The sentence makes much better sense if "Boy" is taken as a typical English exclamation of mild surprise like "Wow", or, in Italian, "mamma mia". I think "cavolo" is the best English approximation.