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

<passage>:
of Earth—and, sooner or later, will happen again! so much as a landslide to bring the Fault to the attention of the low as five people per square mile! The land was so dry it seemed impossible that it could ever be used except for sheep-farming. The even more ironic solution to the problem began in the summer of interested. Seismologists were reporting unusual activity in the area, tremors too severe to be rock slides. Volcanic activity? Specifically, a dust volcano? Unusual, they knew, but right on the Kiowa Fault—could be. It may seem odd that the simplest explanation was practically not mentioned. Only Joseph Schwartzberg, head geographer of the Department of the Interior, wondered if the disturbance might not be a settling of the Kiowa Fault. His suggestion was mentioned on page nine or ten They found, of course, that Schwartzberg had been perfectly correct. They found themselves on the scene of what was fast becoming the most violent and widespread earthquake North America—probably the world—has ever seen in historic times. To describe it in the simplest terms, land east of the Fault was settling, and at a precipitous rate. Rock scraped rock with a whining roar. Shuddery as a squeaky piece of chalk raked across a blackboard, the noise was deafening. The surfaces of the land east and west of the Fault seemed no longer to have any relation to each other. To the west, tortured rock reared into cliffs. East, where sharp reports and muffled wheezes told of continued buckling and dropping, the earth trembled downward. Atop the new cliffs, which seemed to grow by sudden inches from heaving rubble, dry earth fissured and trembled, sliding acres at a time to fall, smoking, into the bucking, heaving bottom of the depression. There the devastation was even more thorough, if less spectacular. Dry earth churned like mud, and rock shards weighing tons bumped and rolled about like pebbles as they shivered and cracked into pebbles themselves. "It looks like sand dancing in a child's sieve," said the scene of disaster. "No one here has ever seen anything like it." And affected area. "When it's over you can come back and pick up the several small tremors everywhere east of the Fault, to almost twenty the danger of rock slides from minor quakes. The geologists went home to wait. to add to the heaving chaos below. And the cliffs were higher every day as the land beneath them groaned downward in mile-square gulps. As the Fault moved north and south, new areas quivered into unwelcome down. They danced "like sand in a sieve" dry, they boiled into rubble. Telephone lines, railroad tracks, roads snapped and simply disappeared. Virtually all east-west land communication was suspended and the President declared a national emergency. Trinchera and Branson were totally evacuated, but even so the over-all On the actual scene of the disaster (or the scenes it is impossible to speak of anything this size in the singular) there was a horrifying confusion. Prairie and hill cracked open under intolerable strains as the land shuddered downward in gasps and leaps. Springs burst to the surface in hot geysers and explosions of steam. floods, in the usual sense. The water moved too slowly, spread itself with no real direction or force. But the vast sheets of sluggish water and jelly-like mud formed death-traps for the countless refugees now streaming east. to be officially admitted that there was an exodus of epic proportion. Nearly two million people were on the move, and the U. S. was faced with a gigantic wave of refugees. Rails, roads and air-lanes were jammed with terrified hordes who had left everything behind to crowd eastward. demand for gas, but once inside the "zone of terror," as the newspapers now called it, they found their route blocked by eastbound cars on the wrong side of the road. Shops left by their fleeing owners were looted by refugees from further west autumn sunshine, growing higher as the land beneath them continued its inexorable descent. On 21 October, at Lubbock, Texas, there was a noise variously described as a hollow roar, a shriek and a deep musical vibration like a church bell. It was simply the tortured rock of the substrata giving way. The second phase of the national disaster was beginning. The noise traveled due east at better than 85 miles per hour. In its wake the earth to the north "just seemed to collapse on itself like a punctured balloon," read one newspaper report. "Like a cake that's of Thayer Street, where the fissure raced through. There was a sigh and a great cloud of dust, and Oklahoma subsided at the astounding rate of about six feet per hour. was somehow to ride out the coming flood, "but like as if the land wanted to be somewhere else." Everyone in doomed Biloxi would have done well to have been somewhere else that evening. At approximately 8:30 p.m. the town shuddered, seemed to rise a little like the edge of a hall carpet caught in a draft, and sank. So did the entire Mississippi and Alabama coast, at about the same moment. The tidal wave which was to gouge the center Mobile, Pensacola, Panama City: 200 miles of shoreline vanished, with over two and a half million people. An hour later a wall of water had swept over every town from Dothan, Alabama, to Bogalusa on the radio message delivered from a hastily arranged all-station hookup. "We of the gallant southland have faced and withstood invasion before." Then, as ominous creakings and groanings of the earth announced the One head of the wave plunged north, eventually to spend itself in by minute the advancing flood bit away miles of river bed, swelling through the night. The earth continued its descent, eventually tipping forming, overtopping the wave's leading edge as towns, hills and the thirst of the soil temporarily broke the furious charge. stopped after inundating Oklahoma City, was being swallowed up in the land was still sinking, and the floods were constantly replenished from great swirl. Whirlpools opened. A great welter of smashed wood and human debris was sucked under, vomited up and pounded to pieces. Gulf-water crashed on rescuers on the cliffs along what had been the west bank of the Pecos River afterwards recalled the hiss and scream like tearing silk as the water broke furiously on the newly exposed rock. It was the most terrible sound they had ever heard. "We couldn't hear any shouts, of course, not that far away and with all the noise," said Dan Weaver, Mayor of Carlsbad. "But we knew there were people down there. When the water hit the cliffs, it was like a collision between two solid bodies. We couldn't see for over an hour, because of the spray." Salt spray. younger children and what provisions they could find—"Mostly a ham and about half a ton of vanilla cookies," he explained to his eventual rescuers. The barn, luckily collapsing in the vibrations as the waves bore down on them, became an ark in which they rode out the disaster. But such lightheartedness and such happy endings were by no means typical. The world could only watch aghast as the water raced north under the shadow of the cliffs which occasionally crumbled, roaring, into the roaring waves. Day by day the relentless rush swallowed what had been dusty farmland, cities and towns. estimated that over fourteen million people had lost their lives. No one could even estimate the damage to property almost the entirety our second California, was unbelievably muggy, almost uninhabitable the Ohio and the truncated Mississippi. remnants of the eight submerged states remained after the flood, but scene. But this is by now no more than a petty annoyance, to raise a smile

<question>:
What was the second phase of the natural disaster?

<options>:
A The falling rock that was giving way.
B The dust clouds that were taking over.
C The flock of refugees seeking safety.
D Annoyingly loud noises that halted progress on rebuilding.

<answer>:

A