question:  Which of these is not a lasting effect of the Ryzgas?
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. 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. I did not see the sleepers, nor will any man until they come again, but I met their sentries, the sentinel machines that guard them now as they have for two thousand years. 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 laid the world waste, stripped it of metals and fuels and bored to its heart for energy, poisoned its seas and its air with the fume of their works, wrung its peoples dry for their labor ... and in each of those four generations they launched a ship of space. "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:  An increase in technological advancements
options:  Climate change on the planet  An increase in technological advancements  Use of limited resources  General fear between groups of people