Final answer:
Nelson Mandela's 'hills' metaphor implies that the journey to achieve human rights is ongoing with many challenges, representing a long, continuous struggle.
Step-by-step explanation:
Nelson Mandela's statement about climbing hills is a metaphor for the ongoing struggle to achieve human rights, indicating that the process is continuous with many challenges ahead. The correct answer is:
D) To achieve human rights requires a long, continuous struggle.
The metaphor highlights that even after overcoming a significant challenge, such as the end of apartheid and Mandela's election as president, the fight for human rights is not over; many more challenges, or 'hills,' remain.