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

<passage>:
Earth set itself grimly to meet them with corrosive fire, determined to blast them back to the stars. But they erred in thinking the Old Ones were too big to be clever. Quest III , as for forty hours the ship had decelerated. nebulae that sprawled in empty flame across light years. But now unwonted excitement possessed the hundred-odd members of the Quest III's crew. It was a subdued excitement men and women, they the same racial characteristics possessed by those aboard the the oncoming star, and there were wide-eyed children who had been born in the ship and had never seen a planet. The grownups talked in low voices, in tones of mingled eagerness and apprehension, of what might lie at the long journey's end. For the Quest III Quest III's captain, came slowly down the narrow but as the immense stores were spent and the holds became radioactively safe, the crew had spread out from its original cramped quarters. Now the interstellar ship was them with an impassive countenance, and announced quietly, "We've sighted Earth." A feverish buzz arose identified it—no more." But this time the clamor was not to be settled. People pressed round remember sunlit skies or grassy fields or woods in summer.... He said, with a touch of tolerant amusement, "What did you think might have happened to Earth? After all, it's only been nine hundred years." "That's just it," said Lesra shakily. "Nine hundred years have gone by— Quests returned successful, or if they returned at all. And we don't know what changes have taken place on Earth. It's possible—not likely, though—that something has happened to break civilization's continuity to the point where our expedition has been The ship's automatic mechanisms had scant need of tending Lesra and the children—but somehow he didn't want to do that either. He felt empty, drained—like his ship. As the Quest III's fuel stores and the hope of success in man's mightiest venture had dwindled, so the Perhaps, he thought, he was feeling the weight of his nine hundred Earth years—though physically he was only forty now, ten years older than when the voyage had begun. That was the foreshortening along the time axis of a space ship approaching the speed of light. Weeks and months had passed for the Quest III in interstellar flight while years and decades had raced by on the home world. since leaving Earth. "Our visit to Procyon drew a blank. There is only one huge planet, twice Procyon had possessed a habitable planet, we could have returned after an absence of not much over twenty years Earth time. "It is cheering to note that the crew seems only more resolute. We go its spectrum, so like our own Sun's, beckons. If success comes there, a century will have passed before we can return to Earth friends, relatives, all the generation that launched the Quest ships "We face the unpleasant realization that what was feared is probably true—that worlds such as the Sun's are a rare accident, and that we may complete our search without finding even one new Earth. "It makes no difference, of course one world in all the Universe. Certainly the building of this ship and its two sisters, the immense expenditure of time and labor and energy stores that went into them, left Earth's economy drained and exhausted. Only once in a long age does mankind rise to such a selfless and transcendent effort—the effort of Egypt that built the pyramids, or the war efforts of the nations in the last great conflicts of the twentieth century. "Looked at historically, such super-human outbursts of energy are the result of a population's outgrowing its room and resources, and Quests . Perhaps our effort will prove as futile as pyramid-building, less practical than orgies of slaughter to very many people to other stars but Earth could at least go into its decline with the knowledge that its race went onward and upward, expanding limitlessly into the Universe.... "Hopeless, unless we find planets!" Omega Centauri is twenty thousand light years away.... "Even so—by expending its remaining fuel freely, the Quest III of aging too greatly. It would be a one-way journey—even if enough fuel remained, there would be little point in returning to Earth after more than forty thousand years. By then our civilization certainly, and perhaps the human race itself, would have perished from memory. "That was why the planners limited our voyage, and those of the other Quests , to less than a thousand years Earth time. Even now, according to the sociodynamic predictions made then, our civilization—if the other expeditions failed also—will have reached a dangerously unstable overpopulation. "Why go back, then with the news of our failure? Why not forget about Earth and go on to Omega Centauri? What use is quixotic loyalty to a decree five thousand years old, whose makers are dead and which may be forgotten back there? Earth, and not even nine hundred years of space and time had been able to alter that. such collisions were rare to the vanishing point. No harm could have been done. The Quest III's collision armor was nonmaterial and for practical purposes invulnerable. interstellar ship. Knowing that Gwar Den was still there, he said, "Now—attacked by what?" "Ships," said Gwar Den helplessly. "Five of them so far. No, there's a Quest III's framework. The There were people running in the corridors, heading for their posts. Their faces were set, scared, uncomprehending. The Quest III shuddered, again and again, under blows that must have had millions of horsepower behind them "Well?" he snapped. "What are they doing?" Gwar Den spoke. "There are thirteen of them out there now, sir, and whatever was hitting the Quest III's shell was doing it at velocities where the distinction between matter and radiation practically ceases to exist. the ship the impact—and the ship, in obedience to the law of equal and opposite The people in the Quest III would have felt nothing at all of the vicious onslaught being hurled against them, save that their Earth. At least, I suspect the answer's there." The Quest III bored steadily on through space, decelerating. Even if one were no fatalist, there seemed no reason to stop decelerating or paying attention to him. The men on the Quest III's bridge looked questions at each other, as the thought of help from outside flashed Quest III , except that they were rocket-propelled and of far lesser size. Their as it occurred to him that perhaps the attackers weren't of human origin. They had seen no recognizable life in the part of the galaxy they had explored, but one of the other Quests might have encountered and been traced home by some unhuman race that was greedy and able to conquer. It became evident, too, that the bombardment was being kept up by a hours." "We'll have reached Earth before then," Gwar Den said hopefully. "If they don't bring out the heavy artillery first." repeating on each the same brief recorded message: "Who are you? What do you want? We are the interstellar expedition Quest III ...." And so on, identifying themselves and protesting that they were unarmed and peaceful, that there must be some mistake, and multiplied demands. Those outside were squandering vastly greater amounts of energy in the effort to batter down its defenses, but from Earth, relayed by one of the midget ships—was not very smart Quest III's ponderous and unswerving progress toward Earth had somehow frightened it. So it was trying to frighten them.

<question>:
Of the following, which is the best plausible explanation for the behavior of the Earthen ships?

<options>:
A Since the Quest III trip promised to locate more planets, the current Earthens didn't trust them when they learned of their success because of how unlikely it was.
B Since the Quest III trip promised to locate more planets, the current Earthens didn't trust them when they learned of their failure.
C Since the Quest III trip promised to locate more natural resources, the current Earthens didn't trust them when they learned of their failure.
D 900 years passed on Earth. The populations were different enough that the Quest III Earthens scared the current Earthen population.

<answer>:

D