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

<passage>:
There should be an epitaph for every Meanings and answers to his questions slithered out of his reach. "Now the world is dead. The whole world is dead." New York lay quietly below him. It was the hour of indecision when day has not quite made up its mind to leave and night has not yet attacked in force. The streetlights were already on, making geometric 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 To any man, WHO HAPPENED TO BE THE LAST MAN ON EARTH! attacking his olfactory patch with the retching smell of decaying flesh. Charles ignored it. Even smells had lost their customary of the sharp pain that raced through his system, in spite of the " Maybe I'm not the last! " ignored it. The street that led towards the Bureau of Vital Statistics 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 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. began dropping as rapidly as the flies which had dropped earlier. Congress was called into special session, as were all of the national governments around the world. The U.N. met at emergency sessions to cope with the situation. The president of the world-wide Society for 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 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 in New York. And now.... "I've got to find out," Charles told himself. He meant it, of course, but in a sense he was afraid—afraid that his trip to the Bureau might 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." The average person had little necessity to do so since the Bureau information service would answer questions free of charge at any time. But he still remembered it and he still recalled the powerful emotional experience it had been those many years ago. All children had to have a brain-wave recording made by the Bureau mechanical wonder had remained with him the rest of his life. of the world. The silence became unbearable. Charles walked to the master control panel. With newly acquired 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 being sampled while the screen would show population density by individual pinpoints of light that merged to form brightness patterns. coward, afraid to check the whole world from the start. "I'll start with New York and work up." 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 not because she liked him, but because.... quickly in on him. His frantic fingers searched for the computer controls. New York State. One. The entire United States. One. The western hemisphere, including islands. (Was that a point of light in Brazil? No. Just a ghost image). One. The Pacific area, Asia, Australia, Asia Minor, Russia and the Near East, Africa and then Europe. England! There was a light in England! Someone else still lived! The counter plague. It's only logical that—" One. Alone. Alone! Why? 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 animals, when he first asked the question: "Why?" free of bodies. that most people wanted to die inside of something—inside of anything. Not out in the unprotected open." The silence was like a weight hanging around his neck. Not an insect of a plane. Not even a breeze to whisper among the leaves, he thought. Civilization equals life equals noise. Silence equals.... earth, me. The last. Why me? the most perfect? Had he led the best of all possible lives? Was that it? Had God, in His infinite wisdom and mercy, spared his life, saved him, singled him out because he was most nearly a saint, most nearly Chance. That was it! The laws of probability, the bell-shaped curve, normal distribution, rectilinear regression. More people per square So simple to explain by the laws of chance. No need for any underlying assumptions about good and evil, no need for teleological arguments to be the last to go and that was— THE LAST MAN ON EARTH Yes. That was it. Simple. Let whoever came afterwards figure out the 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." part of his mind clamped down, obscuring the thought, rejecting the 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! tearing down the defenses of his mind, putting an end of his thoughts of immunity. Colors flared before his eyes, a persistent, irresistible susurrus flooded his ears. 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 Charles struggled to end his body's disorganized responses, to everything else seemed irrelevant: he had he forced his body to become an unwilling Charles refused to think. Machines, especially half-broken machines, do they only work. Sweating, straining, bleeding, retching, he for the grave. Instantly the thought struck him with paralyzing devastation. The sapped the last bit of his energy, corroding his nerves and dying 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. no system. How was "Beautiful," said the first. "It went according to the strictest They made it easy for me." "All right. Let's go." "What's that you have there?" "Oh, this?" replied the first. "It's a higher neural order compendium THE LAST MAN ON EARTH—

<question>:
What did the beings use to ensure they killed every human?

<options>:
A Charles's brain-waves
B The Bureau's Index
C A machine they brought from their home planet
D Spies throughout the world

<answer>:

B