The excerpt tells us that (B.) the people were unfriendly and suspected anything that entered their territory to be an enemy, and that (D.) their entire population was wiped out by infighting and the inability to trust other people.
"The Gun" written by Philip K. D*ck tells the story of a group of space explorers that decide to visit a planet that had been once inhabited by humans. They carry out their investigation, but once they are determined to return home, the group is shot down. This leads them to think that the humans that had lived there had been paranoid and unfriendly because they had created an automated gun that made possible to fire at anyone who passed by. Moreover, this excerpt shows that the explorers believe that humans must have been mistrustful and hostile.