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

<passage>:
ain't gonna do. "That's the problem. All we got to do is figure out the answer. No use making a pircuit, because a puzzle circuit is just a miniature computer with the solution built in if you can build the pircuit, you've old, orange sun. It was a spaceship, but not the kind men had once dreamed about. The flivver was shaped like a crude bullet, blunt at one end of a fat cylinder and tapering abruptly to a point at the other. It had been slapped together out of sheet metal and insulation board, and it sold, fully equipped, for $15,730. It didn't behave like a spaceship, either. As it hurtled down, its speed increased with dramatic swiftness. Then, at the last instant before impact, it stopped. Just like that. Inside the big, central cabin, Grampa waved his pircuit irately in the Grampa was a white-haired 90-year-old who could still go a fast round "Now, Grampa," Fred soothed, but his face was concerned. Fred, once called Young Fred, was Grampa's only son. He was sixty and his hair had Grampa started to say something, but an 8-year-old boy looked up from the navigator's table beside the big computer and said, "Well, gosh, Junior, that's why we picked this planet. We fed all the orbital data into Abacus, and Abacus said that orbital perturbations indicated that Junior had won her was, to Grampa, the most hopeful thing he had ever Grampa was still waving his puzzle circuit indignantly. "See!" The "Anybody talks about gravitational pull," Grampa said, snorting, "deserves anything anybody could say about him. There's no such thing, "Go back to your games, Grampa," Fred said impatiently. "We've got work Grampa knitted his bushy, white eyebrows and petulantly pushed the last "That's right, Four," Grampa muttered, "so I did. But whose money "You bought it, Grampa," Fred said. "That's right! And who invented the gravity polarizer and the space flivver? Eh? Who made possible this gallivanting all over space?" "You, Grampa," Fred said. galaxy? You, Grampa!" "Well, now," Grampa protested, "I got a little put away yet. You'll be "You're never going to die, Grampa," Joyce said harshly. "Just "Well, now," said Grampa, blinking, "how'd you find out about that? computer where Grampa's chair stood. "You brought that pircuit from Grampa looked up, obviously relieved to drop his act of intense "Don't be a kibitzer!" Grampa snapped. "When I need help, I'll ask for it. No dad-blamed machine is gonna outthink Grampa!" He snorted Joyce stood up indignantly. "Well! And don't call me 'Grammy!' It makes at Grampa. "If you'd rather have that blob than me—well!" She swept Grampa glanced warily at Joyce's door to make sure it was completely "Why, thanks, Grampa," Reba said, surprised. "I like you, too, Grampa. If you'd been a few years younger, Junior "You bet he would!" Grampa leaned back and cackled. Then he leaned and to himself, too." Reba smiled at Grampa brilliantly. "And maybe I Grampa turned red and looked quickly toward Four. The boy was staring "It was easy," Grampa said breezily, "once you understood the four each—" "That's right," Four agreed. "I can make you a new one by cannibalizing the other pircuit, but I'll need a few extra parts." Grampa pushed the wall beside his chair and a drawer slid out of it. "What is that stuff you drink, Grampa?" Four asked. "Yep," Grampa said. "Too easy." "Sounds good, boy," Grampa said eagerly. "Whip it up for me." paused at Grampa's feet. Grampa reached down to pat it. For an instant, his hand disappeared As if in response, the flivver vibrated. Grampa looked querulously few low-grade iron deposits and that's it." "Then what makes this planet so heavy?" Reba asked. glared venomously at Grampa. "It's these '23 models," Grampa put in disgustedly. "They never were spaceship rested on its improbable stern. The sixteen Earth hours that the rotation had taken had changed nothing inside the ship, either. Grampa looked up from his pircuit and said, "If I were you, Junior, I Grampa snorted. "Broken-shmoken. Nothing to break, Young Fred. Just a about polarization itself. How does it work, Grampa?" Grampa gave him a sarcastic grin. "Now you're curious, eh? Couldn't be bothered with Grampa's invention before. Oh, no! Too busy. Accept "Let's not get up on any pulpits," Fred growled. "Come on, Grampa, Grampa looked at the four faces staring at him hopefully and the around itself. That's how we've always known it until the invention of spaceships and later the polarizer. The polarizer polarizes gravity into a straight line. That makes the ship take off and continue accelerating until the polarizer is shut off or its angle is shifted." longer. "That's just nonsense! You all know it. Grampa's no genius. "Now wait a minute!" Grampa protested. "That's not fair. Maybe "And then you spent everything you got from it on those fool perpetual-motion machines and those crazy longevity schemes when any Grampa squinted at her sagely. "That's what they said about the gravity "Well, no," Grampa admitted. "Actually I was just fiddling around with "Well, now," Grampa said in bafflement, "it rightly should, you know." "I like your spunk, Reb," Grampa muttered. "Here." Four came through the airlock and trudged across the room, carrying a curious contraption made of tripod legs supporting a "He's why the flivver won't work. What Grampa invented was a linear The land of the Fweep rotated once on its axis, and Grampa lowered "Not now, Grampa," Four said inattentively as he watched Fweep making "I don't figure it's a whim," Grampa said. "Circular gravity is what he's got to have for one reason or another, so he just naturally bends the space-time continuum around him—conscious or subconscious, I don't know. But protoplasm is always more efficient than machines, so the flivver won't move." Grampa lowered his bottle and smacked his lips. "Well, boy," he said to "Give her one for me!" Grampa called. "Makes you think, doesn't it?" Grampa said, looking at Fweep benignly. "Linear polarization is uncomfortable for him, is it?" Grampa said. "Less than some I've known," Grampa conceded. "Well, now," Grampa said maliciously, his eye on Joyce, "that's no "Joyce!" Reba cried, horrified. "Grampa was joking, but you actually won't work." "I'm sure that calling it names won't help, and besides, you shouldn't expect a machine to do something that we can't do. And if it did work, planet, we'll stay here until Four has a beard as white as Grampa's!" Grampa lowered the nippled bottle from his lips and chortled. "Junior, "I take it all back," said Grampa. "That computer won't help you with

<question>:
What is Grampa’s claim to fame?

<options>:
A Striking radioactive deposits on far flung planets that can be sold back on Earth for a fortune
B Solving all the pircuits he’d ever been challenged with
C Being the first space missionary
D Creating a special piece of machinery for spaceships

<answer>:

D