Answer:
B. brave
Step-by-step explanation:
You can use the process of elimination to find the answer, which automatically eliminates C, silent. If Collins was silent, se would not be advocating for sending humans into space and colonizing mars. Popular could also be eliminated, because if there are some people who don't agree with humans being sent out to space, then those people are most likely not going to like Collins, nor does this paragraph mention anything about popularity, as well as loneliness. So B, brave would be the best choice since despite the many dangers of humans being sent out to space, Collins still thinks people should be sent out to space.
I hope this helps and have a great day!