What Is the Difference Between a Dirty Bomb (RDD) and a Nuclear

What is the difference between a dirty bomb (RDD) and a nuclear bomb?

A) Dirty bombs are full of dirt and waste - they are used by environmentalists trying to call attention to the amount of trash we have. Nuclear bombs are used by real terrorist groups.
B) A dirty bomb uses explosives to disperse radioactive material over a large area, a nuclear bomb creates an explosive chain reaction from fissionable nuclear material.
C) Nuclear bombs explode radioactive material to spread it out over an area as big as a city, and dirty bombs are just another name for an EMP.
D) A dirty bomb requires the use of a nuclear power plant, but nuclear bombs can be made mostly from materials found in hardware stores.