Read the following passage and questions, then choose the right answer from options, the answer should be one of A, B, C, D.

<passage>:
Extensive research did not uncover any evidence that the U.S. copyright on this publication was renewed.] Rootless and footloose, a man in space can't help admittance to any office you need to visit tonight. Therefore, it is impossible for me to be of any assistance to you." but dream of coming home. But something nobody should "I—I—" Craig muttered, fumbling in his pockets. a key into the door and opened it for him. "I can get you a sensatia-tape," whispered the boy when they had "No specific destination," supplied the man as he punched a key on a small instrument, "Air-lock ahead and to your right. Strip and follow the robot's orders. Any metal?" motivated by envy soothed him as he clumsily let himself into the lock. "Place your clothing in the receptacle provided and assume a stationary position on the raised podium in the center of the lock." Craig obeyed the robot voice and began reluctantly to remove his flight operation. "You will find a red button at your feet. Lower your head and depress that button." Stepping on the button with his bare foot produced an instant of that was all there was to the sterilizing process. "Your clothing and effects will be in the dressing room immediately beyond the locked door." "You mean you haven't been in a gravity system?" "Oh, I've landed a few times, even walked around for a while...." "With the help of paraoxylnebutal," supplied the captain. "Well, sure." "So I gathered." The captain laughed reassuringly. "No, don't put up your guard again. The worst is over. Short of Gravitational conditioning, there is nothing to stop you from going to Terra." "Sorry, I guess I'm a little touchy. This is my first time...." "Quite natural. But it being your first time—in quite a number of ways, I might add—it will be necessary for you to undergo some conditioning." "Conditioning?" asked Craig. "Yes. You have spent eleven years in space. Your body is conditioned to a normal state of free fall, or at best to a state of acceleration." "Yeah, I know. Once on Gerymeade...." "You were ill, couldn't keep your balance, felt dizzy. That is why all spacemen carry PON, paraoxylnebutal, with them. It helps suppress certain physiological reactions to an entirely new set of conditions. Channels of the ear, for example. They play an important part in our awareness of balance. They operate on a simple gravity principle. Without gravity they act up for a time, then gradually lose During the days that followed, the psychologist seemed to Craig to become progressively more didactic. He would deliver long speeches about the "freedom of open space." He spoke repetitiously of the "growing complexity of Terran society." And yet the man could not be pinned down to any specific condition the spaceman would find "Yet you are so completely sure you will want to live out your life so badly, let them get somebody else. I've put in my time." when the best of 'em want out." Craig clenched the iron rung of his bed and struggled to bring the old "How ... how do they know when you ought ... to come out?" he asked between waves of nausea. "Blood pressure. They get you just before you go into shock." "That strap around your belly. You mean you ain't noticed it?" "Haven't noticed much of anything." "Well, it's keyed to give them some kind of signal." conditioning process. Slowly at first, the lines formed by seams in the metal ceiling began to bend. Here it came again! "Maybe that ain't scientific, but it's the way I always think of it." "Can't they ... drop it down continuously?" "They tried that a few times—once when I was aboard. You wouldn't like it, kid. You wouldn't like it at all." "How ... many times ... do they drop it?" "Four times during the day, three at night. Twenty days." vaguely aware of the moans of other men in the vaultlike room. Wave upon wave of nausea swept him as he watched the seam lines bend and warp fantastically. He snapped his eyelids shut, only to begin feeling the nightmarish bodily sensations once more. He felt the cot slowly "... got it bad." "We better take him out." "... pretty bad." "He'll go into shock." "We better yank him." "I'm ... all right," Craig mumbled at the voices. He struggled with the over him. Four elongated eyes peered at him. Attendants coming for to take me home.... "Touch me and I'll kick your teeth in!" he yelled. "I'm going to Terra. Wish you were going to Terra?" Most of the men had passed through the torments of gravitational conditioning. The huge headquarters base centrifuge aboard the man-made satellite had gradually caused their bodies to respond once more to a single source of pull. They were now ready to become inhabitants of planets again, instead of free-falling ships. On the eighteenth day, automatic machinery freed them from their imprisoning cots. Clumsily and awkwardly at first, the men began to walk, to hold their heads and arms in proper attitudes. They laughed and joked about it and kidded those who were slow at adjusting. Then they again began taking paraoxylnebutal in preparation for the free-fall flight to Terra. Only one of the score of men in the centrifuge tank remained voluntarily in his cot. looking away. "Pick something to talk about. What do you figure on doing when you get to Terra, for instance?" up. The sea tanned their skins and stiffened their bones, but it never stiffened their hearts. When they got old, it just pulled them in. "But space is different. Space is raw and new. It tugs at your guts. It sends the blood rushing through your veins. It's like loving. You don't become a part of space the way you do the old sea, though. It leaves you strictly alone. Except that it sucks you dry, takes all the soup out of you, leaves you brittle and old—old as a dehydrated piece of split leather. "Then one day it shoots a spurt of blood around in one of your old veins. Something gives. Space is through with you then. And if you can stand this whirligig conditioning, you're through with space." " " " " " Yeah, you got to watch the ones that don't. Especially the old ones. " " He's old. You think it was his heart? " " " " They'll dump him, won't they? " " " " " " difficult to fit into the place he had made for it. Exasperated, he refolded it and jammed it in place. Smaller rolls of underclothing were then fitted in. When he was satisfied with the layer, he tossed in a small handful of crystals and began to fill the next layer. After the carton was completely filled, he ignited the sealing strip and watched It was the signal for relief in the passengers' quarters many were beginning to feel a reaction to the short free-fall flight from the with me, but she wouldn't go. Earth was a lot different then than it is now. They don't have to tell me transfer I made out. It isn't much out of seventy years of living, but she may need it. And maybe you can tell her a little bit about what it means to be out there. Tell her it's open and free and when you got hold of those levers and you're trying for an orbit on something big and new and green.... Hell, you remember. You know how atmosphere. He was about to step off the last step when a man appeared hurriedly. A "You mean he screened me? What for?" "Hard to say," the other passenger said. "You'll get used to this. They get it over with quick." "Yes, so big. And also...." He seemed to consider many words before completing the sentence. "And also different."

<question>:
What is the purpose of paraoxynebutal?

<options>:
A It relaxes the sympathetic nervous system
B It puts a human to sleep for up to 12 days
C It helps people adjust to changes in gravity
D It opens the airways to allow for easier breathing

<answer>:

C