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

<passage>:
They packed their meager belongings while Dick finished his meal the sun was high when they left the beach. They followed the shore line southward, the ground rising steadily before them. And before evening, Bobby couldn't help wishing Pop would stand up just a little bit straighter. Not that he was ashamed of Pop it wasn't that at all. It was just that the Patrolman stood so and firm. Standing beside him made Pop look sort of thin and puny chest caved in like he was carrying a heavy weight on his shoulders. Even if he was big and sturdy and broad-shouldered in his space blues. Mom said, "Bobby, what are you muttering about? Do stop fidgeting!" Bobby said, "Yessum," and glared at Moira, as if she, in some obscure way, were to blame for his having been reprimanded right out here in the middle of Long Island Spaceport, where everybody could hear and laugh at him. But Moira, studying the handsome S.S.P. man Bobby bounded forward. "Can I push the button, can I, Pop? When we do anything, everything at once. He took The Pooch into the circle of his left arm, helped his mother aboard, said, "Shut up, kid, you're enough to wake the dead. Watch that guard-panel, Elly. Papers all set, Pop?" And he tickled The Pooch's dimpled cheek with an oily finger. "You act just like your mama," he said irrelevantly, and the baby place, wheezing asthmatically. Bobby's ears rang suddenly with the mild compression of air when he swallowed, they were all right again. Dick saw him. "What are you doing here, kid? Didn't I hear Pop tell you to come below?" Bobby said, "I'm not a kid. I'm almost sixteen." "Just old enough," promised Dick, "to get your seat warmed if you don't mutiny, and—" "I'm obeying," said Bobby hastily. He followed his brother down the the stops and dials, told him which button to press. "When I give the word, kid." Of course, he got to sit in the pilot's bucket-chair, which was something. Moira and Eleanor and Mom to lie down in acceleration hammocks while Pop and Dick sat in observation seats. He waited, all ears and nerves, as the slow seconds sloughed away. Pop set the hypos running their faint, dull throb was a magic sound in the silence. Then there came a signal from outside. Dick's hand rose in understanding response fell again. "Now!" Bobby jabbed the button in frantic haste. Suddenly the silence was absorbing the shock. Across the room a faulty hammock-hinge squeaked rustily. Then it was over as quickly as it had begun, and he could breathe again, and Dick was lurching across the turret on feet that wobbled queerly because up was down and top was bottom and everything was funny But Pop was standing by the observation pane, eyeing an Earth already ball-like in the vastness of space. Earth, dwindling with each passing moment. Bobby moved to his side and watched Moira, too, and Eleanor and Mom, and even Dick. panes at the flame-dotted pall of space—until Pop tried to turn his must not enter certain chambers, that he mustn't push his nose into things that didn't concern kids— Which offended Bobby, who was sixteen, or, anyway, fifteen and three-quarters. with impudent shrewdness—were so much wasted energy, since they were settling in a place where nobody could see them. And Mom bustled about Pop said, "You deserve a great deal of credit, son, for your fine work Frankly, I don't get it! Eros must have terrific mass to have the Roaring craters, Pop, we're rich! Bloated plutocrats!" Bobby did not need to hear Pop's reply to know that it was. His swift to get all dewy-eyed about, like Pop was. Dick said softly, "All right, Pop. Let's check and get ready to set 'er down...." Only it wasn't. Nor did they have any warning that the problem was more complex until it was too late to change their plans, too late to halt "Well, blast me for an Earth-lubbing idiot! Do you see that, Pop?" Pop looked like he had shared Dick's persimmon. "The night-line. We forgot to consider the diurnal revolution." "And now we've got to land in the dark. On strange terrain. Arragh! I should have my head examined. I've got a plugged tube somewhere!" Grampaw Moseley hobbled in, appraised the situation with his incomparable ability to detect something amiss. He snorted and rattled his cane on the floor. "They's absolutely nothin'," he informed the walls, "to this hereditation stuff. Elst why should my own son an' his son be so attraction seized them tighter and tighter until they were completely under its compulsion. Dusk swept down upon them, the sunlight dulled, will stand a lot of bust-up. It's tough. A little bit of luck—" But there was perspiration on his forehead, and his fingers played over the control banks like frightened moths. Through howling Bedlam they tumbled dizzily and for moments that were ages long. While Dick labored frantically at the controls, while Moira watched with bated breath. Mom said nothing, but her hand sought Pop's Eleanor cradled The Pooch closer to her. Grampaw scowled. And then, suddenly— "Hold tight! We're grounding!" cried Dick. And instinctively Bobby braced himself for a shock. But there was only a shuddering jar, a lessening of the roar that beat upon their for the first time in days the Cuchulainn was completely motionless. Dick grinned shakily. "Well!" he said. "Well!" Pop unbuckled his safety belt, climbed gingerly out of his hammock, Pop stroked his chin. He said, "Well, we've landed safely, Richard. But Dick cried, "Hey, this is bad! We'd better get out of here—" Mom cried, "But—but our supplies, Dick! What are we going to do for That's right. There's room for you and The Pooch—" The water was almost ankle deep in the control room by the time they had all donned spacesuits. Bloated figures in fabricoid bulgers, Pop , they fled. The airlock was small. There was room for but one at a time. The water was waist—no, breast-deep—by the time all were gone save Bobby and Dick. Bobby, whose imagination had already assigned him the command of the last to leave. But Dick had other ideas. He shoved Bobby—not too gently—into the lock. Then there was water, black, solid, forbidding, had even been frightening. Throughout the night, the Moseley clan huddled together there on the beach, waiting, silent, wondering. But when the sun burst over the horizon like a clamoring, brazen gong, they The night did not last long. But Pop had told them it would not. His words dwindled into silence, and, inexplicably, Bobby felt awed. It was Grampaw Moseley who burst the queer moment into a thousand spluttering fragments. Grampaw Moseley wiped his mouth with the back of his hand. There were no napkins, which suited him fine. Four Eros days—the equivalent of forty-two Earth hours or so—had passed since their crash landing. In that short time, much had been done to make their beach camp-site comfortable. All members of the Pop said seriously, "I'm afraid you'll have to eat them and like them over-supplied." He thought for a minute. "If that's the way it is, we might as well move." "Move?" demanded Grampaw. "What's the matter with the place we're at?" Pop?"

<question>:
Why was Pop's posture so poor?

<options>:
A It only appeared so compared to the S.S.P. man.
B He was carrying a large item.
C Because of his work doing scientific research.
D He had been standing in line all day.

<answer>:

C