PBL means students are doing work that simulates what happens in the world outside of school. In a project that is somewhat authentic, students could play a role (as in choice "c" above) -- scientists, engineers, advisors to the President, website designers, etc. -- who are placed in a scenario that reflects what might actually occur in the real world. Or students could create products that, although they are not actually going to be used by people in the real world, are the kinds of products people do use.