The educational requirement for a registered nurse at the lowest level would be B. an associates degree. A bachelors degree would be a step up for the RN but if I'm not mistaken, you can go straight to a 4 year college for a BSN (Bachelor's in Science of Nursing).
A. would not be correct because that is what is called an LPN (Licensed Practical Nurse) those are nurses but not registered nurses. There are certain things LPN's may not do that a RN may; like administering narcotics and some are not authorized to start IV's unless they take a separate specialized certificate course.