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

<passage>:
STRANGE EXODUS By ROBERT ABERNATHY 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? Westover got a shock when he stumbled onto the monster, for all that he knew one had been through here. He had been following the high ground toward the hills, alternately could see the rest—the immense slug-like shape that extended in ponderous repose across the river valley, its head and tail spilling over the hills on either side, five miles apart. The beast was quiescent until morning—sleeping, if such things slept. And that explained the flood 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 himself, gasping and quivering, to comparative safety on the broad shelf that marked the rim of the foot. Above him lay the great black steep that rose to the summit of the monster's humped back, a mountain 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 Earth to attack out of all the planets of the Solar System, shows they 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, 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 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 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 monster would begin to move, to crawl eastward impelled by the same dim phototropic urge which must guide these things out of the interstellar depths to Sun-type stars. All of them had crept endlessly eastward 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 still lived and wandered over the once populous fertile lands, like this—would not live long. shape, as the vast protoplasmic mass below crawled, flowed beneath its integument. In slow peristaltic motion the waves marched eastward, 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 the experiments necessary to prove his theory of how to destroy the monsters—if only someone had had the foresight to build a biological laboratory on the monster's back. Of course the rolling motion would create special problems of technique.... Idiocy.... Once more he seemed 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 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 on a dog. The monster crawled by day and rested by night strengthened, before he recognized the wrongness, and when he did he sat bolt upright. The sun was already up, and the monster should have begun once more its steady, ravenous march to the east. But there was no motion the great in deserts or oceans. And his was a stranger solitude than any of those. 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 because of their gaudy cellulose-plastic armor.... The monster on which Westover had been living as a parasite was generating gases within itself, preparing to leave the ravished Earth. That was the meaning of its gargantuan belly rumblings. And they meant 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 line, and lay now in what to it was shallow water—fifty or a hundred fathoms. Back the way it had come, a headland was visible, mockingly, hopelessly distant. Of course—the great beast would crawl into the sea, which would float its bloated bulk and enable it to accelerate and take flight. It would 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 as they had come into the Solar System—in that close, seemingly 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 nodded in childlike obedience, and followed. When, a few hundred yards nearer the monster's head, the other halted at a black rent in the rugose hide, the mouth of a burrow descending wild hope were real. "Down here. Into the belly of Leviathan," said the old man solemnly, and Westover nodded this time with alacrity. The crawling descent through the twisting, Stygian burrow had much that ought to belong to a journey into Hell.... More than that, no demonologist's imagination could have conceived without experiencing moment squeezing in to trap them unspeakably. The air was warm and rank with the familiar heavy sweetish odor of the monster's colorless 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 one way out—to transfer our parasitism to the only remaining food source—the monsters themselves. 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 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 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—"

<question>:
Where was the safest place to be on Earth?

<options>:
A On a mountain
B On top of a monster
C Where the monsters had already been
D Where the monsters were headed

<answer>:

B