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

<passage>:
WHEN THE MOUNTAIN SHOOK steep were its cliffs and sheer its crevasses. But its outward perils could not compare with the Ryzgas themselves, who slept within, ready to wake and conquer.... At sunset they were in sight of the Ryzga mountain. Strangely it towered and fell in a heap, like a mechanical doll whose motive power has Is our feud finished, or does your ambition for a worthy son-in-law go beyond the conqueror of the Ryzgas?" mountain. Var sensed her fear, and the love that had conquered it. He was no longer a simple problem to Var, who had grown much older in the last days. "Wait," he commanded. While she waited he spun a dream, attaching it to lurid fire spewed from the Ryzga mountain, and strange lights dipped above it avalanche in the dream, and hideous beasts rushed snapping and ravening from the crevices of the rock. There was no path. Now they were descending the steeper face of the the rocks above. They heard no sound. watch on the Ryzga mountain, as a part of the oldest legends of their childhood but neither had been here before. a tinkling of falling water, thawed from the glacial ridges above to off and forced us into the mountains, and now they are only a few hours Mountain Watcher. I must be above feuds and families." and on all men." "We know the stories," Var said brusquely. "In the hollow heart of their 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." farther into the mountain than anyone before, farther even than did the 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 as the world has not seen before or since. 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 of their shaping—the scattered wreckage of the things they made. 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. "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 the naked skeletons of buildings and were followed by thunder and a shaking of the earth. poured a mad, hating horde. The recurrent flashes lit scarred faces, naked bodies blackened and maimed from the hell of the workshops where the Ryzgas' might had been forged, eyes that stared white and half sightless from the glare of the furnaces, gnarled hands that now at long last clutched the weapons of the last rebellion—a rebellion without hope of new life on a world gutted and smoldering from the fulfilment of the Ryzgas' dream, without slogans other than a cry for blood. Before them death waited around the citadel where the masters still fought. All round, from the lowest and most poisonous levels of the lightning blazed, and the city howled and screamed and burned. white globe soared upward, rising swiftly without sound. through—before. With deep respect now he gazed upon the bent old man who was the Mountain Watcher. "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 old time, because I must make sure that you do not approach the mountain in ignorance. Our world is unwise and sometimes evil, full of arrogance, folly, and passion that are in the nature of man. Yet it is a happy world, compared to that the Ryzgas made and will make again." gripped him. He had not slept since childhood, and he had forgotten how "You made us fall asleep. Groz will be on us—" Watcher." "Don't thank me. I take no sides in your valley feuds. But now you are rested, your minds are clear. Do you still mean to go on to the Ryzga mountain?" Not looking at the Watcher, Var muttered unsteadily, "We have no The glacial slope on which the cavern opened faced toward the mountain. the morning sun, but the mountain of the Ryzgas drank in the light and gave nothing back. Below their feet the slope fell away into an opaque sea of fog, filling 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 last on the cindery slope of the great volcanic cone, they sensed that little had the Ryzgas feared those who might assail them in their sleep. Var sent his thoughts probing beyond the curtain, listened intently, head thrown back, to their echoes that returned. The tunnel beyond mountain something snapped suddenly alert—something alive yet not for the two on the mountainside the world turned upside down, the of currents behind what appeared to be a blank tunnel wall, a rising Then they felt the mountain begin to tremble. A very faint and remote vibration at first, then an increasingly potent shuddering of the floor was in the Earth was rising great wheels commenced to turn, the mechanical servitors of the Ryzgas woke one by one and began to make ready, while their masters yet slept, for the moment of rebirth that might be near at hand. neither would yield, though the mountain above them and the world outside should crumble to ruin around them. They plunged deeper into the mountain. And the shaking of the mountain Through the slow-rolling thunder of the hidden machines seemed to echo the death-cries of a billion slaves, the despair of all flesh and blood the two invaders felt the rapid shifting of magnetic fields, the fury of electrons boiling in vacuum.... conveyed a queer suggestion of weariness or weakness, as if he were yet not wholly roused from his two millenia of slumber. But the Ryzga's manner and his mind radiated a consciousness of power, a pride and assurance of self that smote them like a numbing blow. With a new shock, Var realized that the Ryzga's thoughts were quite open. They had a terse, disconnected quality that was strange and unsettling, and in part they were couched in alien and unintelligible progression of logical thought, came a wave of raw emotion, devastating in its force. It was a lustful image of a world once more obedient, crawling, laboring to do the Ryzgas' will— toward the stars, the stars! The icy calculation resumed: "Immobilize these and the ones indicated in the passage above. Then wake the rest...." Var was staring in fascination at the Ryzga's face. It was a face formed by the custom of unquestioned command Between the Ryzga and the control panel a nightmare shape reared up seven feet tall, flapping black amorphous limbs and flashing red eyes 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 efforts, as he strove to free himself from the neural hold, were as wrestle with the mind. Var had guessed right. When Neena in her terror had flung a dream monster into the Ryzga's way—a mere child's bogey out of a fairy tale—the Ryzga had not recognized it as such, but had taken it for a real being. Var laughed aloud, and with great care, as one communicates with an infant, he projected his thoughts into the other's mind. "There our world, Ryzga! In two thousand years, we've learned some new things. Now at last I understand why you

<question>:
What causes the shaking of the mountain?

<options>:
A The awakening of the Ryzgas
B Machines
C Earthquakes and tremors
D Dreams spun by the Ryzgas

<answer>:

B