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

<passage>:
By ROBERT ABERNATHY Gigantic, mindless, the Monsters had come out of the U.S. copyright on this publication was renewed.] Westover got a shock when he stumbled onto the monster, for all that he knew one had been through here. Westover stood motionless in the blackness nights without stopping came to his rescue. Westover plodded forward, pressed his shrinking body against the slimy, faintly warm surface of the monster's foot, and sought above him with upstretched hands—found holds, and began to climb with a strength he had not known was left in him. not make that ascent and face the long and dangerous descent beyond, which he had to make before dawn ... but not now ... not now.... He lay in a state between waking and dreaming, high on the monster's side Westover had been one of the men who, in the days when humanity was is all multicellular, on the monsters' home world conditions must have favored unicellular growth. Probably as a result of this unspecialized structure, the monsters have attained their great size and perhaps for the same reason they have achieved what even intelligent cellular life so far hasn't—liberation from existence bound to one world's surface, monsters have finished with Earth, there will be no vegetation left for man's food, no houses, no cities, none of the fixed installations Westover awoke, feeling himself bathed by the cold sweat of made his mind clearer than it had been for days, and he remembered that he could not sleep but had to go on, searching with a hope that would not die for some miraculously spared refuge where civilization and science might yet exist, where there would be the means to realize his idea for stopping the monsters. He sat up, eyes searching the sky for a sign to tell him how long he monster would begin to move, to crawl eastward impelled by the same dim phototropic urge which must guide these things out of the interstellar human pride, the star-storming pride of mind and will—defeated by sheer bulk and mindless hunger. Near the crest of the monster's back, he stumbled and fell hands and knees on the shagreen-roughness of the skin toward the monster's head. He could stay where he was unharmed, of course. On the monster's back, of all places, he had nothing to fear from it or from others of its kind. But he knew with desperate clarity that by nightfall, when the head. It occurred to him that he was now ideally located to conduct the experiments necessary to prove his theory of how to destroy the to glimpse Sutton's face, as the biologist calmly made that grisly report to the President's Committee on Extermination.... Sutton's prediction had been a hundred percent correct. The monsters' hunger knew no halt until they had absorbed into themselves all the organic material on the world which was their prey.... And men must starve, as expand into hope. Fingers shaking, he unhitched the light ax from his belt and began to hack with feverish industry at the monster's crusted hide. The scaly, weathered epidermis seemed immeasurably thick. But at last Clawing and hewing in the hole he had made, he tore out heavy slabs of the monster's flesh. A ripple that did not belong to the crawling motion ran over the like a flea, he had lodged on a larger animal and was about to nourish himself from it. The slabs of flesh he had cut off were gray and unappetizing, but he knew from the studies he had helped Sutton make that the monsters, extraterrestrial though they were, were Then he was tormented by thirst. It was some time, though, before he could bring himself to drink the colorless fluid that had collected in the wound he had inflicted on the monster. Thus began for him a weird existence—the life of a parasite, of a flea on a dog. The monster crawled by day and rested by night strengthened, the man could have left it then, but somehow night after night he did only source of food he knew in all the world—not just that he was developing a flea's psychology. He was a man and a scientist, and he was conducting an experiment.... His life on the monster's back was proving something, something of vast importance for man, the extinct animal—but for increasingly longer periods of time he could not that in the living animal could be under exceedingly high pressures, and that could be expelled to drive the monster in flight like a The monster on which Westover had been living as a parasite was the fresh breeze and sniffing the air he recognized the salt tang of the sea. While he slept the monster had crept beyond the coast that blue headland could be only a land made desert, where men become beasts fought crazily over the last morsels of food. He had lost track of the days he had been on the monster's back, but the rape of Earth must be finished now. He had no doubt that the things would depart Westover sat for a space with head in hands, hearing the faint "Help! Here I am! Help!" He paused to listen with fierce intentness, and heard nothing but the faint eructations deep inside the monster. Then he sprang to his feet, gripping his hand-ax, and ran panting to the place where he had dug for food. His excavations tended to close and heal overnight the latest one, hacking and tearing it deeper and deeper. He was almost hidden in the cavity when a shadow fell across him from behind. He whirled, for there could be no shadows on the monster's back. "Who are you?" asked Westover, breathlessly but almost without surprise. Westover hesitated. "I'm not just imagining you?" he appealed. Westover was still not sure that the other was more than one of the told Westover better than words that there was something hugely destruction from up there.... But I got out in one piece and started walking—looking for some place with people and facilities that could try out my method of killing the monsters. I thought—I still think—I had a sure-fire way to do that—but I didn't realize then that it was Westover finished the brief account of his coming to dwell on the "I haven't got so far with the theory," said Westover, "but I think from the beginning. But the monsters absorbed into themselves all the plant food and even the organic material in the soil. So we have only one way out—to transfer our parasitism to the only remaining food source—the monsters themselves. "The monsters almost defeated us, because of their two special adaptations of extreme size and ability to cross space. But man has Sutton gestured at the bubbling device behind him. "That thing is making air now, which we're going to need when the monster's in space. It was when we were still trying to find a poison for the beasts that I its blood flowing through the filters. We've got an electric generator running by tapping the monster's internal gas pressure. There are problems left before we'll be fully self-sufficient here—but the monster is so much like us in fundamental makeup that its body contains all the elements human life needs too." "Then," Westover glanced appreciatively around, "it looks like the main Westover flexed his hands involuntarily, like one who has been too from an endoparasite's point of vantage, merely by isolating from the creature's blood over a long period enough of some potent Westover stared. "Why?" "No! Of course I realize—Well, I see what you mean—I think." Westover we'll do better to model ourselves on the humble tapeworm. "Your idea is dangerous for the same reason. The monsters probably spend thousands of years in interstellar space during that time monsters capable of supporting a very limited number of people each—with your method giving an easy way to destroy these little Westover bowed his head, but he had caught a curiously expectant glint the end, I see.... This phase of our history won't last forever. Eventually, the monsters will come to another planet not too unlike

<question>:
Why should Westover not kill the monster?

<options>:
A He needs it to destroy the earth
B He needs it to travel to find other people
C He needs it to save the human race
D He needs it to find other monsters

<answer>:

C