question:  Of the following, which is the best plausible explanation for the behavior of the Earthen ships?
context: The great chamber, a full cross-section of the vessel, had been at first a fuel hold. At the voyage's beginning eighty per cent of the fifteen-hundred-foot cylinder had been engines and fuel; but as the immense stores were spent and the holds became radioactively safe, the crew had spread out from its original cramped quarters. He said, with a touch of tolerant amusement, "What did you think might have happened to Earth? He had already set up on the calculator a course that would carry them to Earth. And we don't know what changes have taken place on Earth. That was the foreshortening along the time axis of a space ship approaching the speed of light. "One light-day out from Procyon, the thirty-third day by ship's time since leaving Earth. "Our visit to Procyon drew a blank. There is only one huge planet, twice the size of Jupiter, and like Jupiter utterly unfit to support a colony. If Procyon had possessed a habitable planet, we could have returned after an absence of not much over twenty years Earth time. 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 will be long since dead. Our generation's dream, humanity's dream, lives in us and in the ship forever...." "One week since we passed close enough to Aldebaran to ascertain that that system, too, is devoid of planets. "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. 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. "Looked at historically, such super-human outbursts of energy are the result of a population's outgrowing its room and resources, and therefore signalize the beginning of the end.
output:  900 years passed on Earth. The populations were different enough that the Quest III Earthens scared the current Earthen population.
options:  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.  Since the Quest III trip promised to locate more planets, the current Earthens didn't trust them when they learned of their failure.  Since the Quest III trip promised to locate more natural resources, the current Earthens didn't trust them when they learned of their failure.  900 years passed on Earth. The populations were different enough that the Quest III Earthens scared the current Earthen population.