question:  Which lingering effect of the Ryzgas' downfall makes life challenging for people like Var and Neena?
context: But its outward perils could not compare with the Ryzgas themselves, who slept within, ready to wake and conquer.... Now, if her father and his kinsmen overtook them, it would be death for Var, and for Neena living shame. Which of the two was worse was no longer a simple problem to Var, who had grown much older in the last days. Var saw with some surprise that all the walls were sheathed in ice—warm to the touch, bound fast against melting by the Watcher's will. Behind them began a tinkling of falling water, thawed from the glacial ridges above to descend sheet-wise over the cave mouth, freezing as it fell into lengthening icicles. Hot food and drink were before them almost at once. Warming to the old man now, Var sketched his and Neena's history briefly. And before very long, I'm sure, I would have performed some deed which Groz would recognize as a worthy exploit, and would thus have healed the feud between our families. The Watcher was broodingly silent; his eyes shifted to Neena, where she nestled by Var's side. Neena returned his gaze without flinching; then she looked sidelong at Var, and her lips curled with a proud and tender mockery. There were tyrannies before the Ryzgas, there was lust for power, and atrocious cruelty; but such tyranny, power, and cruelty as theirs, had never been known. They ruled the Earth for four generations, and the Earth was too little for them. They were great and evil as no other people has been, because they wanted the stars. "Because of them we must build with dreams instead of iron, and our only fire is that of the Sun, and even now, two thousand years later, the Earth is still slowly recovering from the pangs and poison of that age. And we—we too are a remnant, the descendants of the few out of all humanity that survived when the Ryzgas' world went down in flame and thunder.
output:  The Ryzgas destroyed or used up all of their materials, so Var and Neena's people can only construct things with their dreams
options:  The Ryzgas littered the planet with wreckage of their old creations, which renders it inhabitable  The Ryzgas destroyed or used up all of their materials, so Var and Neena's people can only construct things with their dreams  The Ryzgas manipulate the entire planet through their Control Center, so all outcomes are predestined  The Ryzgas toxified the environment, which has caused a genetic mutation among their descendants