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

<passage>:
"Ivy?" when we got back ... well...." T.R.S. Aphrodite designing job." Cob waved an expressive arm in the air. "But dammit, man, I thought...." "The answer is no Planet Stories Winter 1948. Extensive research did not uncover any evidence that the U.S. copyright on this publication was renewed.] . Ivy's a nice girl ... but...." He paused and Strike shook his head. "She's gone to the Bureau of Ships with a for two-thirds of the 720-hour day had stopped at last, but now a Aphrodite Aphrodite's and he had been with her a full year ... which was a record for Execs on the Aphrodite breakdowns in half that time. "The same." "Well," Cob ran a hand over his chin speculatively, "I know Gorman's Ganymede . And, after all, you come from an old service family and all that. How come this?" He indicated the monitor expressively. Strike sighed. "Well, now, Cob, I'll tell you. You'll be spacing with me and I guess you've a right to know the worst ... not that you wouldn't find it out anyway. I come from a long line of very sharp operators. Seven generations of officers and gentlemen. Lousy with tradition. "The first David Farragut Strykalski, son of a sea-loving Polish Medal winner. Then came David Farragut Strykalski, Jr., and, in the abortive Atomic War that terrified the world in 1961, he won a United Nations Peace Citation. And then came David Farragut Strykalski III ... me. "From such humble beginnings do great traditions grow. But something happened when I came into the picture. I don't fit with the rest of them. Call it luck or temperament or what have you. "In the first place I seem to have an uncanny talent for saying the astrophysicist warned me that Procyon A might go nova. I left my routine post and loaded up on colonists." He shrugged. "Wrong guess. No nova. I made an ass of myself and lost the Ganymede after the Ganymede broke the record for the Centaurus B-Earth run, Aphrodite's nether belly affectionately. "She's old ... but she's loose. And we're not likely to meet any Ambassadors or Admirals with her, either." . "She'll carry the mail, I suppose. And that's about all that's expected of her." Cob shrugged philosophically. "Better than tanking that stinking rocket fuel, anyway. Deep space?" And she was not an inspiring sight. The fantastically misnamed Aphrodite planner's view. In those days, interstellar astrogation was in its formative stage, and at the time of the Aphrodite's Artemis , the Andromeda too appealing to their hot little hands. They used it ... in some way, wrongly. The Artemis exploded. The Andromeda vanished in the general Aphrodite's store of vicious energy spinning like a Fourth of July pinwheel under tangled, pulpy mess within her pressure hull. The Aphrodite Regulations, tradition and Admiral Gorman of the Inner Planet Fleet required it. And it was now up to David Farragut Strykalski III to see to it that she did.... Strike felt vaguely uncomfortable. He knew, of course, that at least a uncomfortable." Cob shrugged. "Celia's the only officer. But about a quarter of our bridge at 600 hours for Captain's briefing. Officer of the Deck will Antigone , and I expect him by 600 hours. In the meantime you'll take over his part of the work. See to it that we are fueled and ready to lift ship by 602. Base will start loading the mail at 599:30. That's about all." Hendricks, I. V. Hendricks, is what the orders say." Cob thought hard for a moment and then shrugged his shoulders. "I. V. Hendricks." He shook his head. "Don't know him." The other officers of the T.R.S. Aphrodite "... and that's about the story. We are to jet within 28,000,000 miles of Sol. Orbit is trans-Mercurian hyperbolic. With Mars in opposition, we have to make a perihelion run and it won't be pleasant. But I'm astrogation has to be accurate to within twenty-five miles plus or minus the shortest route. And there'll be no breaking orbit. Now be especially in the hydroponic cells. Pure air is going to be important." "That's about all there is to tell you. As soon as our rather leisurely E/O gets here, we can jet with Aunt Nelly's postcard." He chronograph, "... in an hour and five." may be able to convince you that the designer of this vessel was not ... as you seem to think ... a senile incompetent." Strike was perplexed, and he showed it. "Why, certainly ... uh ... Miss ... but why should you be so...." Aphrodite ten hours behind schedule, and Strike and Evans, the Astrogation Officer, were sweating out the unforeseen changes introduced into the orbital calculations by the time spent in free-fall. The Aphrodite dedicating her life to proving her father right and Brass-bottom wrong. There's nothing in the cosmos to nurture friendship like a common enemy. At 30,000,000 miles from the sun, the Aphrodite's refrigeration Lachesis and the Atropos . The two dreadnaughts were engaged in coronary research patrol ... a purely routine business. But the thing that made Strike curse under his breath was Celia Graham's notation that the Atropos carried none other than Lachesis . The Atropos had burst a fission chamber and was falling into the sun. Radiation made a transfer of personnel impossible, and the Atropos power of the Lachesis' but they could not possibly arrive on time. And it was doubtful that it ! This is that line even if he fries himself." skyhigh three times out of three. Very neat." desperate. "But we can save those ships! We can, I know we can! My father designed this ship! I know every rivet of her! Those idiots off and save those ships!" Her expression turned to one of disgust. "Or are you afraid?" "Frankly, Ivy, I haven't enough sense to be afraid. But are you so certain that we can pull this off? If I make a mistake this time ... it'll be the last. For all of us." "We can do it," said Ivy Hendricks simply. Strike turned to Cob. "What do you say, Cob? Shall we make it hotter in here?" Whitley shrugged. "If you say so, Strike. It's good enough for me." Celia Graham left the bridge shaking her head. "We'll all be dead soon. Lashed together with a length of unbreakable beryllium steel cable, Lachesis and the Atropos fell helplessly toward the sun. The frantic flame that lashed out from the Atropos . It plunged together. They were diving into the sun. The heat in the Aphrodite's out of the cable. Blackness was flickering at the edges of her field of vision. She could scarcely lift her hand to the red-sealed circuit "I ... I ... can't make it ... Strike. You'll ... have to run ... the show ... after ... all." found them. The three ships ... Atropos , Lachesis cold from the acceleration, and Aphrodite's tanks bone dry. But they "All I said to him...." "I know. I know what you said ... and it won't bear repeating. But about Ivy?"

<question>:
Why is a day 720 hours long?

<options>:
A The day length is set such that their mission only takes one day to increase morale
B Day length is dependent on the solar system the ship is in
C A day is equivalent to a month at the speed they travel
D It’s not known

<answer>:

D