The correct answer is: C. Either I or II is implicit.
The statement “Imprisonment for 27 years made Nelson Mandela, the President” does not imply that only those who are imprisoned for 27 years will become president, nor does it imply that imprisonment is a qualification for becoming president. It is possible that there are other factors that contributed to Nelson Mandela becoming president, such as his leadership skills, his charisma, and his popularity. It is also possible that there are other people who have been imprisoned for 27 years who have not become president. Therefore, both assumptions I and II are possible, but neither is necessarily true.