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

<passage>:
"I mean," she explained, "maybe you should ask why people in the 20th did want to go to worlds men are not suited to inhabit." Maitland felt his face become hot. "Men can go anywhere, if they want the U.S. copyright on this publication was renewed.] To the men of the future, the scientific why goals of today were as incomprehensible "But to logic. "Living space, for one thing. The only permanent solution to the population problem...." "We have no population problem. A hundred years ago, we realized that the key to social stability is a limited population. Our economic system was built to take care of three hundred million people, and we have held the number at that." "Birth control," Maitland scoffed. "How do you make it work—secret police?" "No. Education. Each of us has the right to two children, and we section of the Reservation slept silently under the pale illumination there's still the adventure of the thing. Surely, somewhere, there must wasn't the California desert! Down the hill, where the liquid oxygen Venus? Wouldn't you like to see the rings of Saturn from, a distance She shrugged her shapely shoulders. "Go into the past—yes! But go out there? I still cannot see why." Where was he? Who had brought him here? For what purpose? He thought he knew the answer to the last of those questions. As from the human race, or a member of the original atomic reaction-motor team, he possessed information that other military powers would very much like to obtain. the heavily guarded confines of the Reservation, yet someone had done it. How? It was absolutely incredible that anyone had managed to abduct him from traveling is the greatest adventure there is. At least, that is the the Age of Technology. Everybody was terribly excited about what could be done with machines—machines to blow up a city all at once, or fly around the world, or take a man to Mars. We have had our fill of—what built apparently from an aluminum alloy, somehow gave the impression of arrested motion. Even after allowances were made for the outlandish function right, we are satisfied to forget about them. design, something about the room still was not right. life and death of cultures than by the expansion or contraction of the ?" movement. What chance would he have? The unfortunate knight would argue in vain that the atomic bomb offered a means of finally destroying the infidel.... Despite his sudden irrational anger toward her, Maitland tried to stick and showed striking muscular development, like persons who had trained for years with weights. They vanished below his field of view, presumably into the building. leave it except when accompanied by myself. You will not be harmed in any way, provided you cooperate. And you can forget the silly idea that we want your childish secrets about rocket motors." Maitland's heart jumped. "My reason for bringing you here is altogether different. I want to give you some psychological tests...." "Your name," said Swarts, "is Robert Lee Maitland. You are thirty-four years old. You are an engineer, specialty heat transfer, particularly as applied to rocket motors.... No, Mr. Maitland, I'm not going to question you about your work just forget about it. Your home town is how would you like to go to the Moon to go to the Moon. I'm interested in finding out why ." There were three questions for which he required answers before he could formulate any plan or policy. Where was he? What was the purpose of the "tests" he was being given? It was possible, of course, that this was all an elaborate scheme for getting military secrets, despite Swarts' protestations to the constellations, but Venus was his favorite. Time and time again he its transient rule there as evening star, its progression toward the Last night Venus hadn't been there. Later, when that jewel of a planet had set and the stars were out, psychological tests at their face value most likely, they were what they purported to be. Only one question of importance remained: What year was this? the greatest adventure imaginable to 20th Century man. cities and busy spaceports, roaring gateways to the planets. Somewhere, out there in the night, there must be men who had walked Venus—somewhere, perhaps, men who had visited the distant luring stars and returned. Surely, a civilization that had developed time travel could reach the stars! And he his life among the planets, a citizen of deep space, a voyager of the challenging spaceways between the solar worlds. "I'm adaptable," he told himself gleefully. "I can learn fast. There'll be a job for me out there...." wouldn't talk, he would have to find a way of forcing the issue. The that she had discarded the white cloak. 3 x dx" in his head. It was a calculation which required great concentration and frequent declared excruciatingly that they couldn't keep that up. all the intelligent social responsibility of a rogue gorilla, but no more. He brooded over the damnable stupidity and short-sightedness of Swarts in standing by his silly rules and not telling him about this aboard a ship dropping in toward Mars, making planetfall at Syrtis In his mind, he circled the Moon, and viewed the Earth as a huge bright globe against the constellations.... of what I want from him. I want to travel in time, go back to your 20th Eagerly he asked, "Why the devil do you want to go to the 20th Century? She shrugged. "Swarts says that I want to go back to the Dark Age of "How do you mean—" Maitland wrinkled his brow—"adapt to modern culture? Don't tell me you're history since 1950. Five hundred years ago, Europe was overrun by eventually conquered all the world, except for North America—the last remnant of the American World Empire—and southern Africa. The Afrikanders had been partly isolated for several centuries then, and they had developed technology while the rest of the world lost it. They had a tradition of white supremacy, and in addition they were terrified of being encircled." She sighed. "They ruled the next world empire and it was founded on the slaughter of one and a half billion human beings. That went into the history books as the War of Annihilation." "So many? How?" "They were clever with machines, the Afrikanders. They made armies of them. Armies of invincible killing-machines, produced in robot shudder. "And yet they founded modern civilization," she added. "The grandsons of the technicians who built the Machine Army set up our robot production system, and today no human being has to dirty his hands raising food or manufacturing things. It could never have been done, either, before the population was—reduced to three hundred million." "Then the Afrikanders are still on top? Still the masters?" "No. Intermarriage. Racial blending. There was a psychology of guilt race now. No more masters or slaves." talk about them any more." transportation? Do you have interstellar flight yet?" "Inter-what?" "Have men visited the stars?" "But tell me about what men are doing in the Solar System. How is life on Mars and Venus, and how long does it take to get to those places?" After several seconds, Maitland swallowed. Something seemed to be the matter with his throat, making it difficult for him to speak. "Surely you have space travel?" She frowned and shook her head. "What does that mean—space travel?" He was gripping the edge of the bed now, glaring at her. "A civilization that could discover time travel and build robot factories wouldn't find it hard to send a ship to Mars!" "A . Why, no, I don't suppose it would be hard. But why would anyone want to do a thing like that?" you know, no one has ever visited the planets, and no one wants to. Is his life to get to Mars. I thought I would in my time. I was positive I obvious to me that whenever men were able to reach the planets, they'd do it." why happened? Why don't men want the planets any more?"

<question>:
Why did they not travel to the other planets?

<options>:
A They had gone in the past
B They had tried to go and failed
C They had no desire to go
D They could not build rockets

<answer>:

C