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

<passage>:
PLANET of DREAD was being marooned on a planet of endless terrors. It seemed insane that such creatures, even in miniature, should painstakingly be brought across light-years of space to the new worlds men settled on. But it had been found to be necessary. The ecological system in which human beings belonged had turned out to be infinitely complicated. It had turned out, in fact, to be the ecological system of Earth, and unless all parts of the complex were present, the total was subtly or glaringly wrong. So mankind distastefully ferried pests as well as useful creatures to its new worlds as they were made ready for settlement. Mosquitos throve on the inhabited globes of the Rim Stars. Roaches twitched nervous antennae on the settled planets of the The humanity spread through the galaxy with an attendant train of insects and annoyances. If they left their pests behind, the total system of checks and balances which make life practical would get lopsided. It Nadine was out of overdrive and all the uncountable suns of the Nadine . Something had been left out of the seeding of this planet. The element—which might be a bacterium or a virus or almost anything at all—the element that kept creatures at the size called "normal" was either missing or inoperable here. The results were not desirable. nowhere else. There was an ice-cap in view. The rest was—clouds. planet's atmosphere. Sulfur dioxide or chlorine, for example, would not allow the formation of water-ice. It would have to be sulphuric-acid or The ice-cap, by its existence and circular shape, proved that the planet rotated at a not unreasonable rate. The fact that it was water-ice told hydrochloric-acid ice. But the ice-cap was simple snow. Its size, too, told about temperature-distribution on the planet. A large cap would much. A water-ice ice-cap said that there were no poisonous gases in the , then approaching the world on planetary drive. He was to be left here, with no reason ever to expect rescue. Two of the watched out the same ports as the planet seemed to approach. Burleigh said encouragingly speaker. It wasn't a voice-signal. It wasn't an identification beacon, such as are placed on certain worlds for the convenience of interstellar skippers who need to check their courses on extremely long runs. This was something else. find a planet and check its climate and relationship to other planets, and its flora and fauna against descriptions in the Directory. That was the way to find out where one was, when one's position became doubtful. The Nadine needed to make a planet-fall for this. "That's a marker," Carol announced. "I saw a costume-story tape once that had that sound in it. It marked a first-landing spot on some planet or other, so the people could find that spot again. It was supposed to be a long time ago, though." galaxy shone steadily, remotely, as infinitesimal specks of light of system had been a vast glaring disk off to port, with streamers and prominences erupting about its edges. Now it lay astern, and Moran could see the planet that had been chosen for his marooning. It was a would not maintain itself. The vagaries that could result were admirably proper company watched as the planet's surface enlarged. The ice-cap cloudy world. There were some dim markings near one lighted limb, but went out of sight around the bulge of the globe, but no markings appeared. There were cloud-banks everywhere, probably low down in the emergency-kit, anyhow." The emergency-kit contained antiseptics, seeds, and a weapon or two, with elaborate advice to castaways. If somebody were wrecked on an even possibly habitable planet, the especially developed seed-strains would provide food in a minimum of time. It was not an encouraging thought, though, and Moran grimaced. off-planet, and fast. But space-travel regulations are especially designed to prevent such escapes. He'd made a pretty good try, at that. One of the controls on space-traffic required a ship on landing to deposit its fuel-block in the space-port's vaults. The fuel-block was not returned until clearance planet from which they'd carried away a criminal, even though they'd done it unwillingly. Investigation of such a matter might last for months. there were other colors, all of them unlike the normal color of vegetation on a planet with a sol-type sun. course in descent. Except for the patches of color, it was the only considerable landmark within the half-mile circle in which anything could be seen at all. shared the peculiarity of the ground as far as they could see through the haze. It was not vegetation in any ordinary sense. Certainly it was no mineral surface! The landing-pockets had burned away three or four feet of it, and the edge of the burned area smoked noisesomely, and somehow it looked as if it would reek. And there were places where it mound was not a fold in the ground. It was not an up-cropping of the ash-covered stone on which the Nadine rested. The enigmatic, dirty-yellow-dirty-red-dirty-blue-and-dirty-black ground-cover hid spare. And meanwhile we'll take a look at that wreck yonder. There might be an indication in it of what solar system this is. There could be suit. Modern space-suits weren't like the ancient crudities with bulging water-soluble gases in the atmosphere, and a gas can't be an active poison if it can't dissolve. They filed out of the airlock. They stood on ash-covered stone, only slightly eroded by the processes which made life possible on this planet. They looked dubiously at the scorched, indefinite substance which had been ground before the Nadine The hole exposed a cheesy mass of soft matter which seemed riddled with small holes. Something black came squirming frantically out of one of the openings. They're—bugs! the galaxy, but that's what they are! what had happened here. He could begin to guess at other things to be discovered. It had not been practical for men to move onto new planets and subsist upon the flora and fauna they found there. On some new planets life had never gotten started. On such worlds a highly complex operation was necessary before humanity could move in. A complete ecological complex had to be built up microbes to break down the rock for soil, bacteria to fix nitrogen to make the soil fertile plants to grow in the new-made dirt and insects to fertilize the plants so they would multiply, and animals and birds to carry the seeds planet-wide. On most planets, to be sure, there were local, aboriginal plants and animals. But still terrestrial creatures had to be introduced if a colony was to feed itself. Alien plants did not supply satisfactory food. So an elaborate adaptation job had to be done on every planet before native and terrestrial living things settled down together. It wasn't impossible that the scuttling things were truly beetles, grown large and monstrous under the conditions of a new planet. And the ground.... "This ground stuff," said Moran distastefully, "is yeast or some sort of toadstool growth. This is a seedling world. It didn't have any life on it, so somebody dumped germs and spores and bugs to make it ready for plants and animals eventually. But nobody's come back to finish up the job." around its middle was dropped a hundred years ago, and more." There was an abrupt thickening of the cylindrical hull at the middle. There was an altogether blame the others. They couldn't land at any colonized world with him on board without his being detected as an extra member of the crew. His fate would then be sealed. But they also would be

<question>:
Why have the planet's life forms developed abnormally?

<options>:
A The dense cloud cover caused them to grow abnormally large.
B The light of uncountable suns caused them to grow abnormally large.
C A sulphuric-acid ice cap caused them to grow abnormally large.
D An element was missing during the planet seeding process. This element would've encouraged normal growth.

<answer>:

D