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

<passage>:
Earth doctor to see that he didn't! [Transcriber's Note: This etext was produced from it. The call from Morua II came in quite innocently, relayed to the ship from HQ in Standard GPP Contract code for crash priority, which meant Top Grade Planetary Emergency, and don't argue about it, fellows, just get there, fast. Red Doctor Sam Jenkins took one look at the call-source like a hound on a fox. The fact that Morua II was a Class VI planet didn't quite register with anybody, just then. Ten minutes later the Red Doctor reached for the results of the Initial Green Doctor Wally Stone frowned and scratched his whiskered chin. "Sounds familiar, but I can't quite tune in. Crash call?" His eye caught the black-striped card. "Class VI planet ... a plague spot! How can we get a crash-call from to establish a Contract with them, and five times we got thrown out bodily. The last time an Earth ship landed there half the crew was summarily shot and the others came home with their ears cut off. Seems the folks on Morua II didn't want a Contract with Hospital Earth. And they're still in the jungle, as far as their medicine goes. Witch doctors and spells." He tossed the Info-card down the chute with a growl. "So now we have an emergency call from them in a Contract code If we still happen to be around later, that is." It had always been that way. Since the first formal Medical Service Contract had been signed with Deneb III centuries before, Hospital Earth had laboriously built its reputation on that single foundation stone: immediate medical assistance, without question or hesitation, whenever and wherever it was required, on any planet bound by Contract. That was the law, for Hospital Earth could not afford to jeopardize a Contract. In the early days of galactic exploration, of course, Medical Services was only a minor factor in an expanding commercial network that drew multitudes of planets into social and economic interdependence but Other planets outstripped Earth in technology, in communications, in transport, and in production techniques—but Earth stood unrivaled in its development of the biological sciences. Wherever an Earth ship landed, the crew was soon rendering Medical Services of one sort or another, whether they had planned it that way or not. On Deneb III the Medical Service Contract was formalized, and Hospital Earth came into being. Into all known corners of the galaxy ships of the General Practice Patrol were dispatched—"Galactic Pill Peddlers" forging a chain of Contracts from Aldebaran to Zarn, accepting calls, diagnosing ills, arranging for proper disposition of whatever medical problems they came across. Serious problems were shuttled back to Hospital Earth without delay more frequently the GPP crews—doctors of the Red and Green services, representing the ancient Earthly arts of medicine and surgery—were able to handle the problems on the spot and by themselves. It was a rugged service for a single planet to provide, and it was costly. Many planets studied the terms of Contract and declined, pleasantly but firmly—and were assured nevertheless that GPP ships would answer an emergency call if one was received. There would be a fee, of course, but the call would be answered. And then there were other planets—places such as Morua II.... The Lancet homed on the dismal grey planet with an escort of eight ugly fighter ships which had swarmed up like hornets to greet her. They triangled her in, grappled her, and dropped her with a bone-jarring crash into a landing slot on the edge of the city. As Sam Jenkins and does not die. We have you here now. You are doctors, you say. Cure him." cannot eat. He moans until the Palace trembles." "What about your own doctors?" Aguar spat angrily on the floor. "They are jealous as cats until trouble comes. Then they hide in the caves like chickens. See the is all over. We have heard about you wizards from Hospital Earth. You cure all, the stories say. You are very wise, they say. You balance the humors and drive forth the spirits of the Pox like devils." He "What kind of freedom?" "We'll need supplies and information from our ship. We'll have to consult your physicians. We'll need healthy Moruans to examine—" "But you will cure him," Aguar said. without a Bio-survey—look what happened on Baron when they tried it! Half the planetary population wiped out before they realized that the "Yeah," said Wally. "What, for instance?" "Well, we've got a little to go on just from looking at them. They're oxygen-breathers, which means they manage internal combustion of carbohydrates, somehow. From the grey skin color I'd guess at a cuprous or stannous heme-protein carrying system. They're carnivores, but god They dug in frantically. Under normal conditions a GPP ship would send in a full crew of technicians to a newly-Contracted planet to make the initial Bio-survey of the indigenous races. Bio-chemists, physiologists, anatomists, microbiologists, radiologists—survey doctor from Sol III. Anatomy was a broad determinant: a jelly-blob from with an organized central nervous system and a functional division of work among organ systems could be categorized, tested, studied, and compared, and the information used in combating native disease. Given no major setbacks, and full cooperation of the natives, the job only For the crew of the Lancet handled external examinations and blood and tissue chemistries Stone ran the X-ray and pan-endoscopic examinations. After four grueling "All right then, what causes it? Do you know? Bacteria? Virus? magic and all. Maybe you were the boys that turned thumbs down so violently on the idea of a Hospital Earth Contract, eh? Couldn't risk promises, pills and post-mortems. That's the Medical service for you." Sam grinned. "Maybe you should operate on him. That "No thanks, not me. This is a medical case and it's all yours. What do you want me to do?" poke holes in the healthy ones! And then you send in this bag of each other like long-lost brothers at a sad farewell. "I finally got through to somebody at HQ," he said as the Red Doctor climbed aboard. "It'll take them twenty days at least, to get help, considering that Morua is not a Contract planet and we're not supposed to be here in the first place, but that's the best they can do...." they've got things all wrong back at HQ." He brandished a huge roll of parchment, stricken through with the colors of the seven Medical Services of Hospital Earth. "Take a look, my boy—the juiciest Medical Services Contract that's been written in three centuries—" He tossed the Contract in the dry-storage locker with a sigh. "Old Kiz just finished his first lesson, and he's still wondering what went on—" "So am I," said the Green Doctor suspiciously. "It was simple. We cured His Eminence of the Pox." "With what? Incantations?" "Oh, the incantations were for the ," said Jenkins. "They expected them, obviously, since that was the only level of medicine aspirin," he said weakly. "And on that you risked our necks." "Not quite," said the Red Doctor. "You're forgetting that I had one other prescription to use—the oldest, most trustworthy healer-of-all-ills known to medicine, just as potent now as it was a thousand years ago. Without it, Hospital Earth might just as well pack up her little black bag and go home." He smiled into the mirror as he adjusted the scarlet band of the Red Service across his shoulders. "We

<question>:
How did Earth come to be the hospital planet?

<options>:
A Earth had the most liquid water to be incorporated into medical treatments
B Earth was the site of a previous wartime hospital, and due to that experience they became known as the hospital planet
C As interplanetary transit developed, planets specialized
D Earth’s atmosphere has a unique ability to soothe many types of illnesses when patients from other planets are brought to Earth Hospital

<answer>:

C