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

<passage>:
Ryzga made a savage, wholly futile effort to lift the weapon in his Dark was the Ryzga mountain and forbidding with the Ryzgas themselves, who slept within, ready to wake and At sunset they were in sight of the Ryzga mountain. Strangely it towered mountain. Var sensed her fear, and the love that had conquered it. He felt a wave of tenderness and bitterness. For him she had come to this. follow him. Now, if her father and his kinsmen overtook them, it would the crags that loomed over the pass, and to the frozen ground underfoot. lurid fire spewed from the Ryzga mountain, and avalanche in the dream, and hideous beasts rushed snapping and ravening ascents, sheets of traitorous glare ice. Place after place had to be crossed on the air, and both grew weary with the effort such crossings cost. They hoarded their strength, helping one another one alone might never have won through. It was starry night already when they saw the light from the Watcher's the rocks above. They heard no sound. The two young people stared for a long minute, intrigued and fearful. Both had heard of this place, and the ancient who lived there to keep watch on the Ryzga mountain, as a part of the oldest legends of their of him, more marred by age than anyone they had ever seen before, was disappointing. They had expected something more—an ancient giant, a off and forced us into the mountains, and now they are only a few hours behind us." "A pity, indeed. I would like to help you—but, you understand, I am the overtaking us. I have only one idea left: we can go where Groz may fear to follow us." "To the mountain, you mean." mountain the Ryzgas sleep, as they chose to do when their world crumbled. But if they are wakened, the mountain will tremble, and the Ryzgas will come forth." "Do you believe that?" "As one believes stories." "It is true," said the Watcher heavily. "In my youth I penetrated farther into the mountain than anyone before, farther even than did the First Watcher. 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. When I had gone that far, the mountain began to shake, the force that is in the Earth rumbled "The Ryzgas also were men," said the Watcher. "But they were such a race the Ryzgas, there was lust for power, and atrocious cruelty 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. those four generations they launched a ship of space. 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. that survived when the Ryzgas' world went down in flame and thunder. "In the last generation of their power the Ryzgas knew by their science that the race of man would endure them no longer. They made ready their weapons, they mined the cities and the factories for destruction, making sure that their works and their knowledge would perish with them. the Ryzgas' might had been forged, eyes that stared white and half the Ryzgas' dream, without slogans other than a cry for blood. "Some of the Ryzgas took flight to the stars, and some perished on Earth. But there was a group of them who believed that their time to rule would come again. These raised a black mountain from the Earth's heart, and in hollows within it cast themselves into deathless sleep, their deathless and lifeless sentinels round them, to wait till someone dare arouse them, or until their chosen time—no one knows surely. "I have told you the story you know, and have shown you a glimpse of the old time, because I must make sure that you do not approach the mountain "You made us fall asleep. Groz will be on us—" "Groz and his people could not detect your thoughts as you slept. They were all night chasing elusive dreams on the high ridges, miles away." mountain?" Not looking at the Watcher, Var muttered unsteadily, "We have no alternative." breeze of morning swept into the cave. The youth beckoned to them, and they followed him outside. the morning sun, but the mountain of the Ryzgas drank in the light and curling fog hid everything. "You have an alternative," said the Watcher crisply. The two took their eyes from the black mountain and gazed at him in sudden hope, but his They thought, in the warm intimacy of unreserved understanding: " It would work: I-you would make the sacrifice of shame and mockery—yet Ryzga mountain." Quickly, he impressed on them what he had learned of the structure of the mountain and of its guardian machines. Var closed his eyes, a little dizzied by the rapid flood of detail. bridges from crag to crag. Groz and his pack, in their numbers, would cross the gorge more surely and swiftly. When Var and Neena set foot at last on the cindery slope of the great volcanic cone, they sensed that the pursuit already halved their lead. They stood high on the side of the Ryzga mountain, and gazed at the doorway. It was an opaque yet penetrable well of darkness, opening into the face of a lava cliff, closed only by an intangible curtain—so little had the Ryzgas feared those who might assail them in their sleep. made it only this far. It was farther than the Watcher had gone into these uncharted regions, and only the utmost alertness of mind and sense had saved them from death in traps like this. But as yet the way was not blocked.... Then they felt the mountain begin to tremble. A very faint and remote vibration at first, then an increasingly potent shuddering of the floor under their feet and the walls around them. Somewhere far below immense mechanical servitors of the Ryzgas woke one by one and began to make knew with finality that the other's stubbornness matched his own—that neither would yield, though the mountain above them and the world outside should crumble to ruin around them. "Follow us, then!" They plunged deeper into the mountain. And the shaking of the mountain increased with every step, its vibrations became sound, and its sound was like that of the terrible city which they had seen in the dream. Without warning, lights went on. Blinking in their glare, Var and Neena room that was likewise ablaze with light. Cautiously they crept forward to the threshold of that chamber at the mountain's heart. Its roof was vaulted its circular walls were lined with panels studded the two invaders felt the rapid Var and Neena huddled frozenly, half expecting each instant to be their last. And the Ryzga too stood motionless, looking down at them. not wholly roused from his two millenia of slumber. But the Ryzga's symbols. But there was no block. Apparently the Ryzga felt no need to crawling, laboring to do the Ryzgas' will— The Ryzga's final thought clicked into place: Ryzga froze, teetering off balance and almost falling, as a numbing grip the Ryzga's frantic eyes. They glared back at him with such hatred and such evil that for an instant he almost faltered. But the Ryzga's tale—the Ryzga had not recognized it as such, but had taken it for a built so many machines, such complicated arrangements of matter and energy to do simple tasks—it was because you knew no other way."

<question>:
Why were the Ryzgas not afraid that someone might enter their mountain?

<options>:
A They did not believe that anyone would want to return to a terrifying society that the Ryzgas left behind
B They commissioned the Watcher to spin dreadful dreams about what might happen if people attempted to do so
C They thought that their descendants would eventually die out without access to raw materials
D They were convinced that no one would be able to penetrate the mountain without advanced technology

<answer>:

D