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

<passage>:
Gigantic, mindless, the Monsters had come out of interstellar space to devour Earth. They gnawed at her soil, drank deep of her seas. Where, on this gutted cosmic carcass, could humanity flee? pressed his shrinking body against the slimy, faintly warm surface of the monster's foot, and sought above him with upstretched hands—found too vast for human intelligence and weapons to defeat.... planet. It was an ordinary face, roundish, spectacled, but etched now poisons are ineffective against them—apart, that is, from the chief reason of sheer size. The creatures are so loosely organized that a local injury hardly affects the whole. In a sense, each one of them is Earth to attack out of all the planets of the Solar System, shows they slime molds are the highest reticular organisms, and the dominant life 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, adaptation, as brainless life once crawled out of the sea to conquer the dry land. "The monsters who have descended on Earth must represent the end result of a long evolution completed in space itself. They are evidently deep-space beings, able to propel themselves from planet to planet and from star to star in search of food, guided by instinct to suns and worlds like ours. Descending on such a planet, they move across its surface systematically ingesting all edible material—all life not mobile enough to avoid their march. They are like caterpillars that overrun a planet and strip it of its leaves, before moving on to the next. "Man is a highly mobile species, so our direct casualties of this invasion have been very light and will continue to be. But when the monsters have finished with Earth, there will be no vegetation left for man's food, no houses, no cities, none of the fixed installations of civilization, and the end will be far more terrible than if we were all devoured by the monsters." Westover awoke, feeling himself bathed by the cold sweat of tenuous and illusory, more the bitter reality of the breaking day. monster would begin to move, to crawl eastward impelled by the same dim phototropic urge which must guide these things out of the interstellar around the Earth, gutting the continents and churning the sea bottoms, and by now whatever was left of human civilization must be starving beyond the Arctic circle, or aboard ships at sea. The hordes that prospect of death that was most crushing, but the death blow to his 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 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 he had chopped through it, reached the softer protoplasm beneath. 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 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 in the basic chemistry of proteins, fats and carbohydrates one with man fire from the loose fibrous scale of the monster's back, and half an hour later was replete. Either the long fast, or involuntary revulsion, or perhaps merely the motion of the creature brought on nausea, but he monster's vitals, and in a flash of insight knew them for what they were. The scientists had found, in the burst bodies of the Titans that had been killed by atomic bombs, the answer to the riddle of these creatures' crossing of space: great vacuoles, pockets of gas that in the living animal could be under exceedingly high pressures, and that could be expelled to drive the monster in flight like a 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 one-willed swarm that Earth's astronomers had at first taken for a "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 the sheer horror of the yielding beslimed walls that seemed every moment squeezing in to trap them unspeakably. The air was warm and rank with the familiar heavy sweetish odor of the monster's colorless blood.... on the face of the Earth. Fundamentally, parasitism—on the green plants and their by-products—was our way of life, as of all animals 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 new ones as the need arose. The greatest crisis humanity ever faced 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 hit on the catalyst that makes their blood give up its oxygen—that's 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." a temporary expedient. Human history hasn't had such a turning-point for the rest of our lives—and our children's and our children's children's—as parasites inside this monster and whatever others we can manage to—infect—when they're clustered again in space." from an endoparasite's point of vantage, merely by isolating from the creature's blood over a long period enough of some potent secretion—hormone, enzyme or the like—to kill when suddenly We don't want to follow the sorry example of such unsuccessful species 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 Earth, and so will we. We've got a whole new history of man ahead proliferate until they kill their hosts. But imagine a struggle for Lebensraum when all the living space there is is a few thousand monsters capable of supporting a very limited number of people each—with your method giving an easy way to destroy these little the end, I see.... This phase of our history won't last forever. Eventually, the monsters will come to another planet not too unlike Earth, because it's on such worlds they prey. A tapeworm can cross the Sahara desert in the intestine of a camel—" His voice was drowned in a vast hissing roar. An irresistible pressure distorted the walls of the chamber and scythed its occupants from their

<question>:
Why is Earth so bleak for human civilization?

<options>:
A The monsters destroyed all of the Americas and Asia
B The monsters killed everyone except for Westover
C The monsters have destroyed most places
D The monsters quickly suck the energy out of humans

<answer>:

C