Which line in this excerpt from “the gun” by philip k. dic is an example of euphemism? the captain peered into the eyepiece of the telescope. he adjusted the focus quickly. "it was an atomic fission we saw, all right," he said presently. he sighed and pushed the eyepiece away. "any of you who wants to look may do so. but it's not a pretty sight." "let me look," tance the archeologist said. he bent down to look, squinting. "good lord! " he leaped violently back, knocking against dorle, the chief navigator. "why did we come all this way, then? " dorle asked, looking around at the other men. "there's no point even in landing. let's go back at once." "perhaps he's right," the biologist murmured. "but i'd like to look for myself, if i may." he pushed past tance and peered into the sight.

A EUPHEMISM, a type of figure of speech, is "a mild or indirect word or expression substituted for one considered to be too harsh or blunt when referring to something unpleasant or embarrassing." 
In this passage their has been an "atomic fission" which the crew is taking a turn looking at through their eye piece/telescope. From what we have read so far, an atomic fission probably refers to some type of weapon, perhaps similar to an atomic bomb. We know that this would create a scene of absolute devastation. It is clear from the reaction of the crew members that what they are looking at is horrifying since one of the people, after looking through the scope, "jumps back violently". Another crew member says that there's "no point in even landing" insinuating that the damage they are seeing is so bad it would not serve a purpose to be there. 
The euphemism, then, is "it's not a pretty sight" which is said by the Captain. If what they are seeing is so awful that the crew members are "violently" shocked and dismayed enough to return around and abandon their mission, "not a pretty sight" is an understatement and substitution of the actual facts made to to lesson the severity of what is real. While euphemism is sometimes used for humorous purposes, in this case it is probably used because the Captain is so disheartened or upset by what he sees. He is probably trying to lessen the desire of the other members to look at the devastation he has seen.