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

<passage>:
patterns through the dusk of Central Park. Some of the billboards were shining, their relays activated by darkness-sensitized solenoids. A reddish-orange pallor hung from the sky. "Why did it have to be her—or me? Why should it have to happen to attacking his olfactory patch with the retching smell of decaying flesh. Charles ignored it. Even smells had lost their customary meanings. were taller, men were healthier, most of the problems of humanity unit of population, each section of town operating on perpetual, ever-lasting, automatic atomic piles. Two years ago the animals had started dying. Strangely enough the rats had gone first, to anybody's notice. Sales of poison dropped, scientific laboratories chained to a perpetual rodent-cycle began to complain bitterly. Then the lovers who hunted out and haunted the lonely lanes through the countryside began to remark that the locusts were late that year. The Southern states joyously reported that mosquito control was working to an unprecedented degree. The largest cotton crop ever was forecast and rumors from Mexico had it that no one had died from scorpion bite in several weeks. the Prevention of Cruelty to Animals committed suicide. Within a year it was obvious to everyone that man was the only animal left on earth. The panic which had begun with the death of the animals was quieted somewhat by the fact that humans seemed immune to the pandemic. But the lakes full of dead fish caused a great stink and residents along the coasts began to move inland. Sales of perfumes and deodorants soared. Then just one year ago, the first human became infected with the strange malady. Within six months, half of the world's population was gone. Less than a month ago no more than a few thousand people remained but in a sense he was afraid—afraid that his trip to the Bureau might give him an answer he didn't dare listen to. "But I've got to try." He walked on down the bloody street. Before the plague the Bureau of Vital Statistics had been one of man's crowning achievements. Housed as it was in a huge metallic globe of a building, it contained computers which kept exact account of every human on earth. Compulsory registration and the classification of each individual by means of the discrete patterns of his brain waves had accomplished for man what no ordinary census could have. The machine knew who was alive, who was dead, and where everybody was. Once a year the Bureau issued The Index, an exact accounting of Earth's four billion inhabitants. Four billion names and addresses, compressed into microprint, a tremendous achievement even for the "Proud Era." dexterity he switched the computer screens on and watched them glow to life. All around the world sensitive receiving stations pulsed to activity, sending out searching fingers, hunting for elusive patterns of neutral energy, mapping and tabulating the results. The main computer screen dominated one wall of the room. Other smaller screens clustered around it. On these screens could be graphed the population of any and every part of the globe. An illuminated counter immediately above it would give the numerical strength of the area Charles activated the switches that would flash a schematic map of New York on the screen. "There's bound to be somebody else left here. After all, there were at least twenty of us just a couple of days ago." And one of them, a beautiful woman, had invited him up to her apartment, not because she liked him, but because.... quickly in on him. His frantic fingers searched for the computer controls. The Pacific area, Asia, Australia, Asia Minor, Russia and the Near East, Africa and then Europe. plague. It's only logical that—" He stopped. For even as he spoke, the light winked out! The counter clicked again. Why? Such a simple question, but in those three letters lay the essence of human nature. Why. The drive of curiosity. Stronger, in a way, than the so-called "basic" drives: hunger, thirst, sex, shelter, warmth, companionship, elimination. Certainly more decisive in the history of the race. Man began to think, to differentiate himself from the other animals, when he first asked the question: "Why?" free of bodies. "You've got about ten minutes warning," he said to himself. "I guess that most people wanted to die inside of something—inside of anything. earth, me. The last. Why me? Chance. That was it! The laws of probability, the bell-shaped curve, So simple to explain by the laws of chance. No need for any underlying assumptions about good and evil, no need for teleological arguments concerning cause and effect. Simply explain it by chance. Somebody had to be the last to go and that was— rejects such things. There must be something beyond mere accident. practice up for things like this. But it ought to be good, it ought to be proper. "'In this now hallowed corner of the planet Earth—' No. That sounds too ... too...." Make it simple, he thought. And he finally wrote: THE LAST MAN ON EARTH Yes. That was it. Simple. Let whoever came afterwards figure out the Somehow, though, since things were ready and it didn't make too much difference, it seemed to Charles that he'd probably have a long time to wait. "Maybe it's just a disease, and I'm immune. I was immune to smallpox. The vaccination never took. That's probably it." He smiled. Strange, but now he wanted very much to go on living, alone or not. There were things he could do, ways to keep occupied. The tantalizing thought of "why" puzzled its way back into his mind. to the restaurant. This was the way the plague began, but—His mind quickly repressed the idea. It couldn't be the plague. He was immune! Another burst of pulsating, shattering pain crashed through his body, tearing down the defenses of his mind, putting an end of his thoughts appealed to every divinity he knew, all the time knowing it would be useless. His body, out of his voluntary control, tried to run off in all directions at once. Charles struggled to end his body's disorganized responses, to stomach protested, he vomited. It made no difference. Charles refused to think. Machines, especially half-broken machines, do they only work. Sweating, straining, bleeding, retching, he pushed himself towards his goal, trying to add one final touch of grace Instantly the thought struck him with paralyzing devastation. The sapped the last bit of his energy, corroding his nerves and dying The world will end, not with a bang, nor with a whimper, but with the last man's anguished cry at the unreasonableness of it all. Charles screamed. The large, invisible, ovular being that hung suspended over the Empire State Building rested from its exertion. Soon it was approached by another of its kind. "I can feel the emptiness of it." "It was very good. Where were you?" "On the next planet out. No beauty to it at all "What's that you have there?" "Oh, this?" replied the first. "It's a higher neural order compendium the Things here made up. It's what I used." "You can't take it with you, you know. They don't allow souvenirs." "All right, all right. You're so good, see if you can compute the scatter probability." The first being moved imperceptably and the heavy plastoid binding of fluttered down into the shallow hole beneath, unnoticed. The writing on the metal, until then partially obscured by the papers, became legible:

<question>:
What is the true cause of Earth’s “plague” and what is its purpose?

<options>:
A The plague was facilitated by aliens, described as invisible, ovular beings. Their purpose is to clear Earth of all life and start their own colony.
B The plague’s true cause is never revealed. Just as Charles suspects at the time of his death, the fall of the human race is completely unreasonable and meaningless.
C The plague was facilitated by aliens, described as invisible, ovular beings. Their purpose is to exterminate all of Earth’s life in order to start their own planetary garden.
D The plague was facilitated by aliens, described as invisible, ovular beings. Their purpose is to move from planet to planet exterminating living systems.

<answer>:

D