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

<passage>:
and then only at the urging of a newly assigned cousin anxious to see cousin's utter disgust. the descendants were scraping bottom now—advised. Martin showed his work in Italy, so that the cousin could be disillusioned by the current crop of Romans. He found that neither purpose nor malice was enough and felt an uncomfortable pang of a sensation he could no longer understand. "Where do you suppose Conrad has been all this time?" Martin idly asked the current cousin—who was passing as his nephew by now. The young man jumped, then glanced around him uncomfortably. "Conrad's a very shrewd fellow," he whispered. "He's biding his time—waiting until we're off guard. And then—pow!—he'll attack!" "Oh, I see," Martin said. He had often fancied that Conrad would prove to be the most stimulating member of the whole generation. But it seemed unlikely that he would Conrad?" "Because he's coming to kill you." them were insane, or what Ninian had told him at first was the truth. They came from the future. When Martin was sixteen, Raymond took him aside for the talk Ninian had promised five years before. "The whole thing's all my brother Conrad's fault. You see, he's an idealist," Raymond explained, pronouncing the last word with distaste. Martin nodded gravely. He was a quiet boy now, his brief past a dim and passing laws to do away with the—well, abuses and things like that, and I'm sure someday everything will come out all right. However, Conrad is so impatient." "I thought, in your world, machines did all the work," Martin suggested. "I've told you—our world is precisely the same as this one!" Raymond snapped. "We just come a couple of centuries or so later, that's all. frightening—his race had lost something vital. Unaware of the near-contempt in which his young ancestor held him, Raymond went on blandly: "Anyhow, Conrad took it upon himself to feel particularly guilty, because, he decided, if it hadn't been for the fact that our great-grandfather discovered the super-drive, we desperate for a fresh topic of conversation." Anyhow, Raymond went on to explain, Conrad had bribed one of Farkas' assistants for a set of the plans. Conrad's idea had been to go back in time and "eliminate!" their common great-grandfather. In that way, there would be no space-drive, and, hence, the Terrestrials would never man, you know." Raymond's expressive upper lip curled. "So Conrad decided to go further back still and get rid of his great-grandfather's father—who'd been, by all accounts, a pretty worthless character." cousins and me—held a council of war, as it were, and we decided it was our moral duty to go back in time ourselves and protect you." He beamed at Martin. The boy smiled slowly. "Of course. You had to. If Conrad succeeded in eliminating cousins possessed to a consternating degree. Martin had, of course, no illusions on that score he had learned long , Martin knew, could have meant anything from blackmail to the use of the iron maiden. "Then we were all ready to forestall Conrad. If one of us guarded you night and day, he would never be able to carry out his plot. So we made sentimentalist like Conrad. Though you do have rather a look of him, you know." Suddenly that seemed to make Conrad real. Martin felt a vague stirring of alarm. He kept his voice composed, however. "How do you plan to protect me when he comes?" that she'd come see him again. She never did, though, except at the very last. Raymond and Martin moved into a luxurious mansion in a remote area. The dozen years later, they weren't touched. Martin was never sure whether this had been sheer luck or expert planning. Probably luck, because his descendants were exceedingly inept planners. "How about a moat?" Martin suggested when they first came. "It seems to go with a castle." "Do you think a moat could stop Conrad?" Raymond asked, amused. "No," Martin smiled, feeling rather silly, "but it would make the place seem safer somehow." The threat of Conrad was beginning to make him grow more and more nervous. He got Raymond's permission to take two suits of armor that several times he fancied he saw them move. He also became an adept with the ray gun and changed the surrounding landscape quite a bit with it, until Raymond warned that this might lead Conrad to them. During those early years, Martin's tutors were exchanged for the higher-degreed ones that were now needful. The question inevitably least twenty of the cousins came back through time to hold one of their vigorous family councils. Martin was still young enough to enjoy such occasions, finding them vastly superior to all other forms of could take you there. I'm sure you would like it." "Don't be a fool, Grania!" Raymond snapped. "Well, Martin, have you to be perfectly frank, I can't quite understand how." "I am not going to sit down and explain the whole thing to you all over again, Bart!" Raymond said impatiently. "Well, Martin?" "What would you suggest?" Martin asked. But the fear did not show in Martin's pictures. They were pretty pictures. Cousin Ives—now that Martin was older, he was told to call the descendants cousin "Takes time," Ives tried to reassure him. "One day they'll be buying your pictures, Martin. Wait and see." Ives was the only one of the descendants who seemed to think of Martin Tourists always like ruins best, anyway." So he drew on the family's vast future resources and bought a yacht, which Martin christened The other cousins appeared to find the yacht a congenial head-quarters, they never moved back to land. Martin spent the rest of his life on The Interregnum . He felt curiously safer from Conrad there, although there was no valid reason why an ocean should stop a traveler through time. More cousins were in residence at once than ever before, because ended in a brawl, because one cousin was sure to accuse another of He rather liked Ives, though. Sometimes the two of them would be alone together then Ives would tell Martin of the future world he had come "Oh," Martin murmured, trying to sound shocked, horrified—interested, even. "Sometimes I'm not altogether sure Conrad was wrong," Ives said, after Conrad, and even he—" Ives looked out over the sea. "Must be a better way out than Conrad's," he said without conviction. "And everything will work out all right in the end. Bound to. No sense to—to anything, if it doesn't." He glanced wistfully at Martin. he couldn't even seem to care. During all this time, Conrad still did not put in an appearance. Martin had gotten to be such a crack shot with the ray pistol that he almost wished his descendant would show up, so there would be some excitement. But he didn't come. And Martin got to thinking.... He always felt that if any of the cousins could have come to realize the basic flaw in the elaborate plan they had concocted, it would have continent, a hundred years or more before the date of his birth. A great many of the cousins turned up at the simple ceremony. All were dressed in overwhelming black and showed a great deal of grief. Raymond cousin from the future a while, Martin couldn't tell one from another. Cousin after cousin came to watch over him and eventually they were as hard for him to tell apart as the different oceans. All the cousins were young, for, though they came at different times in his life, they had all started out from the same time in theirs. Only the young ones had been included in the venture

<question>:
What is the flaw in the cousins' plan?

<options>:
A Conrad could target their great-great-grandmother and achieve the same result.
B Conrad could target their great-grandmother and achieve the same result.
C They have kept Martin isolated for almost his entire life, he has no son. Therefore, they will cease to exist.
D All Conrad needs to do to find Martin, is to follow the cousins back in time.

<answer>:

C