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

<passage>:
Rikud looked out upon the garden and he trembled. Out there was life. The garden stretched off in unthinkable immensity to the cluster of low mounds against the bright blue which roofed the many plants. If plants could live out there as they did within the world, then so could Every day for a week now, Rikud had come to the viewport to watch "There is Rikud on the floor!" Tugging at the handle of the door, Rikud pulled himself upright. viewport and Rikud imagined it turned to look at him with two hideous Rikud screamed and hurtled back through the corridor, and his face apparent in the speckled profusion Rikud had always known. Instead, If he had understood the term, Rikud would have told himself this was Rikud got up and ran. He reached the door again and then he slipped Rikud knew he should be exercising now, or bathing in the rays of the his heart pounded hard and he felt the pulses leaping on either side of his neck. He stared out into the garden, and off into the distance, where the weight of his body with all his strength against the door. It opened and he stepped outside into the warmth. The air was fresh, fresher than any air Rikud had ever breathed. He walked around aimlessly, touching the plants and bending down to feel tube. Rikud, for his part, wanted to get back to the viewport and watch Rikud muttered to himself and undressed. The world had begun to annoy was a strange thought, and Rikud's brain exciting. He liked them. He liked the garden, for all its hugeness. With so many people, and especially now with women, he was not afraid. It was much better than the small world of machinery, buzzer, Rikud had been stopped in this action, although there was no real Rikud felt at home. before Rikud's time, had negated the necessity for a knowledge of Rikud looked at that foot, it was with a sense of satisfaction. True, proved the world was not perfect. Rikud was guiltily glad when he saw This was a new thought to Rikud, and he propped his head up on one "You know," Rikud said, sitting up now, "the stars in the viewport are channelings of Rikud's energy in new and confusing directions. The view had changed, and the strangeness of it made Rikud's pulses where Rikud had seen the one bright central star, he now saw a globe of Presently Rikud became aware that his eyes were not tearing any longer, A few moments more, and Rikud no longer could see the sphere. A section Startled, Rikud leaped back. The sullen roar in the rear of the world But Rikud forgot the old man completely. A new idea occurred to him, the viewport. the viewport. That was maddening. Rikud turned again to the port, where he could see Rikud whirled on the little figure and pointed to the swirling cloud of Anger welled up inside Rikud. "All right," he said, "listen. What do Now the vapor had departed, except for a few tenuous whisps. For a moment Rikud thought he could see the gardens rearward in the world. Rikud sat down hard. He blinked. The world had come to rest on the garden of the viewport. For a whole week that view did not change, and Rikud had come to accept it as fact. There—through the viewport and in it—was a garden. A garden larger than the entire world, a garden of plants which Rikud had never seen before, although he had always liked to stroll through the world's garden and he had come to know every plant well. Nevertheless, it was a garden. He told Chuls, but Chuls had responded, "It is the viewport." he admitted to Rikud. "But why should the garden be in the viewport?" Somehow, Rikud knew this question for a healthy sign. But he could not tell them of his most amazing thought of all. The change in the viewport could mean only one thing. The world had been walking—the word seemed all wrong to Rikud, but he could think of no other, unless it were running. The world had been walking somewhere. That somewhere was the garden and the world had arrived. "It is an old picture of the garden," Chuls suggested, "and the plants are different." "Then they've changed?" "Well, what about the viewport? Rikud regretted that he never had had the chance to read that book on obvious. If he, Rikud, walked from one part of the world to another, health-rays. Now if the world had walked from—somewhere, through the vast star-speckled darkness and to the great garden outside, this also was purposeful. The world had arrived at the garden for a reason. But if everyone lived as if the world still stood in blackness, how could machine and book on astronomy or stars in his lap, Rikud approached the There's nothing. It just isn't. It's only a door, Rikud." Rikud saw a small room, perhaps half a dozen paces across, at the other Rikud heard a voice not unlike that of the reading machine. Only this one was different. In it Rikud saw the viewport. But how? The viewport stood on the other end of the world. It did seem smaller, and, although it looked out on the garden, Rikud sensed that the topography off in the distance. And this door one could walk through, into the garden. Rikud put his hand on the door, all the while watching the garden through the new viewport. He began to turn the handle. Then he trembled. What would he do out in the garden? He couldn't go alone. He'd die of the strangeness. It was a silly garden again. Not when he knew there was a door through which he could walk and then might find himself in the garden. It was so big. A buzzer sounded and automatically Rikud found himself releasing Chuls. In a moment, the room was cleared. Rikud stood alone. He cleared his This frightened Rikud, although he didn't know why. He'd like it, would the buzzer stop? It probably would, because, as Rikud saw it, he casual. Soon his easy strides had given way to frenzied running. Rikud Rikud never wanted to do anything more than he wanted to open that All around Rikud were darkness and hunger and thirst. The buzzer did eat or drink. Rikud himself had fumbled through the blackness and the thing you did, Rikud." "It was not bad. The world has moved through the blackness and the stars and now we should go outside to live in the big garden there beyond the viewport." "That's ridiculous," Chuls said. Rikud was sad. Soon he would die, because no one would go outside with frond and tasted it. It had been bitter, but not unpleasant. Maybe the plants in the viewport would even be better. "We will not be hungry if we go outside," he said. "We can eat there." "We can eat if the buzzer sounds, but it is broken," Chuls said dully. "We must go outside—through the viewport." Rikud listened to the odd The hand reached out again, and it struck Rikud hard across the face. and the feet pounding behind him, and he wanted only to get away. It was dark and he was hungry and everyone who was strong enough to run was chasing him, but every time he thought of the garden outside, and how big it was, the darkness and the hunger and the people chasing him were unimportant. It was so big that it would swallow him up completely and positively. He became sickly giddy thinking about it. But if he didn't open the door and go into the garden outside, he would die because he had no food and no water and his stomach gurgled and grumbled and hurt. And everyone was chasing him. Rikud tripped over something and sprawled awkwardly across the floor.

<question>:
What does the viewport allow Rikud to realize?

<options>:
A There is more to the world outside of the ship they are on.
B The viewport is not a flat space, and objects can pass through it.
C The stars are indeed changing.
D The garden outside is moving.

<answer>:

A