A robot may break down. Also, it takes robots much longer to cover the same amount of ground than it would a human. Think how much faster we could learn about the planet if we sent humans to work alongside the robots!
Finally, claims that there will be significant health problems for people who travel to Mars are wrong. Studies have shown that radiation levels on Mars are not lethal to humans. Sure, we would have to live in a dome at first, but over time, we could use science to change the atmosphere and make it possible to go outside, just like on Earth! The choice is clear. We need to go to Mars now!
It's C as the climax is when the story is most exciting. Its C as it says there's high stakes and ratchets up tension which in return make the story very exciting.
