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. in miniature form on other worlds. Enlarged like this. It seemed insane that such creatures, even in miniature, should painstakingly be brought across light-years of space to the new worlds 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 Coal-sack. Dogs on Antares had fleas, and scratched their bites, and humanity spread through the galaxy with an attendant train of insects and annoyances. If they left their pests behind, the total system of 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 The ice-cap, by its existence and circular shape, proved that the planet 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 hydrochloric-acid ice. But the ice-cap was simple snow. Its size, too, told about temperature-distribution on the planet. A large cap would have meant a large area with arctic and sub-arctic temperatures, with much. A water-ice ice-cap said that there were no poisonous gases in the rotated at a not unreasonable rate. The fact that it was water-ice told thick, dense cloud-masses which covered most of the surface,—all the surface, in fact, outside the ice-cap. But since there were ice-caps small temperate and tropical climate-belts. A small one like this meant wide tropical and sub-tropical zones. The fact was verified by the such as are placed on certain worlds for the convenience of interstellar seem to resent what he'd tried to do, or that he'd brought them an of space-travel, any criminal anywhere could escape the consequences of effect, with six people on board instead of five, the find a planet and check its climate and relationship to other planets, The Nadine needed to make a planet-fall for this. that had that sound in it. It marked a first-landing spot on some planet could see the planet that had been chosen for his marooning. It was a proper company watched as the planet's surface enlarged. The ice-cap cloudy world. There were some dim markings near one lighted limb, but possibly habitable planet, the especially developed seed-strains would off-planet, and fast. But space-travel regulations are especially planet from which they'd carried away a criminal, even though they'd rivulet ran between improbable-seeming banks. There were a few very small hills of most unlikely appearance. It was the ground, the matter on which one would walk, which was strangest. It had color, but the vegetation on a planet with a sol-type sun. stone. The walls of the hollow were black and scorched. It seemed that at some places they quivered persistently. 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 much louder. Something hooted, maintaining the noise for an impossibly "What's that stuff there, the ground?" he demanded. "We burned it away in landing. I've seen something like it somewhere, but never taking the place of grass!" Then, instantly he'd said it, he recognized that it could be true. The 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 something. It blurred the shape it covered, very much as enormous suit. Modern space-suits weren't like the ancient crudities with bulging nowadays. A man could move about in a late-model space-suit almost as 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. It was eight or ten inches long. It had a head, a thorax, and an cheese-like, curd-like stuff. More black things squirming to view in obvious panic. They popped out everywhere. It was suddenly apparent that the top of the soil, here, was a thick and blanket-like sheet over the whitish stuff. The black creatures lived and thrived in tunnels under it. They're—bugs! They're beetles! They're twenty times the size of the beetles we humans have been carrying around the galaxy, but that's what they are! 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 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." a foot thick and ten feet long, and it had a group of stumpy legs at its "We're looking at an inch-worm, grown up like the beetles only more so. creature more widely than most. destroy it. Thick fumes arose, and quiverings and shakings began. Black creatures in their labyrinths of tunnels began to panic. Off to the right the blanket-like surface ripped and they poured out. They scuttled men—the armed ones—moved back from the smoke. They wore space-helmets size and registration. The world they came from would claim them as

<question>:
What is the most likely reason that creatures on the alien planet have grown to such a large size?

<options>:
A The planet is being used by the government as a site to breed creatures that could keep the population in check.
B The planet's atmosphere comprises gases that target the DNA of living creatures, causing them to grow in size.
C The planet, like many others, is being used as a site to copy a habitable eco-system, but has been left unchecked.
D The planet's cheesy, perforated ground is made up of a substance that causes living creatures to mutate.

<answer>:

C