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

<passage>:
The Last Monster Irgi was the last of his monster race, guardian of a dead planet, master of the secret of immortality. It was he whom the four men from Earth had to conquer to gain that secret—a tentacled monstrosity whom Earthly weapons could not touch. [Transcriber's Note: This etext was produced from the opalescent mists that bathed the city in shimmering whiteness. They hung low, those wispy tendrils of mist, clasping everything in their clinging shelter, destroying dust and germs. Irgi had discovered the mist many years ago, when it was too late to save his kind. bands of cobalt that sped outward from the cones. He preened his body then spread outwards, all over his huge form. Irgi was immortal, and the blue light made him so. the law of nature. It would atrophy, otherwise. grey eyes bored like a steel awl downward at the mighty globe swinging in the void. "The last planet in our course," he breathed. "Maybe it has the radium!" "Yes," whispered the man beside him, wetting his lips with his tongue. "No use to think of failure. If it hasn't, we'll die ourselves, down there." Radium. And the Plague. It had come on Earth suddenly, had the Plague, back in the first days of space travel, after Quigg, the American research scientist at Cal Tech, discovered a way to lift a rocket ship made the first flight through space, died of cancer. As the years passed to a decade, and the ships of Earth rode to Mars and Venus, it began to be apparent that a lifetime of space travel meant a hideous death. Scientists attributed it to the cosmic rays, for out in space there was no blanketing layer of atmosphere to protect the fleshy tissues of man from their piercing power. It had long been a theory that cosmic rays were related to the birth of new life in the cosmos perhaps they were, said some, the direct cause of life. Thus by causing the unorderly growth of new cells that man called cancer, the cosmic rays were destroying the life they had created. It meant death to travel in space, and only the stupendous fees paid to the young men who believed in a short life and a merry one, kept the ships plying between Mars and Earth and Venus. Lead kept out the cosmic rays, but lead would not stand the terrific speed required to lift a craft free of planetary gravity and an inner coating of lead brought men into port raving with lead poisoning illusions. Cancer cases increased on Earth. It was learned that the virulent form of space cancer, as it was called, was in some peculiar manner, contagious to a certain extent. The alarm spread. Men who voyaged in space were segregated, but the damage had been done. The Plague spread, and ravaged the peoples of three planets. Hospitals were set up, and precious radium used for the fight. But the radium was hard to come by. There was just not enough for the job. A ship was built, the fastest vessel ever made by man. It was designed for speed. It made the swiftest interplanetary craft seem a lumbering barge by comparison. And mankind gave it to Valentine Emerson to take it out among the stars to find the precious radium in sufficient quantities to halt the Plague. It had not been easy to find a crew. The three worlds knew the men were going to their doom. It would be a miracle if ever they reached a single planet, if they did not perish of space cancer before their first goal. Carson Nichols, whose wife and children were dying of the Plague, begged him for a chance. A murderer convicted to the Martian salt mines, Karl Mussdorf, grudgingly agreed to go along on the promise heralded cancer. Involuntarily, he shuddered. Mussdorf scowled darkly, and spat. "A hell of a way to spend my last days," he growled. "I'm dying on my trap, and bellowed. A hail from the depths of the ship answered him. A "For what? How do we know what they're like? An inhabited planet doesn't mean men. We found that out—several times." "We can hope," said Emerson sharply. "Maybe they have some radium, stored so that our spectroscope couldn't pick it up." germs. No dust. Just clean air!" Emerson leaped to his side, staring, frowning. "No germs. No dust. Why—that means there's no disease in this place! No disease." He began to laugh, then caught himself. "No disease," he whispered, "and every one of us is going to die of cancer." Mussdorf came up through the trap and passed out the sun-blasters. They buckled them around their waists while Mussdorf swung the bolts of the It was coming across the square, flowing along on vast black tentacles "Lord," whispered Mussdorf. "What is it?" The thing dropped the Earthmen suddenly his sun-blaster—felt it ripped from his fingers, knew a hard blackness thrashing down at him. He went backwards, sickened.... eyes were caught suddenly by the lumps protruding from their arms and legs, from face and chest. The growth disease! That was bad, but Irgi knew a way to cure it. Irgi knew a way to cure anything. Perhaps the metal of the hull had in some manner made his voice audible to them, speeded up the vibrations to twelve or fifteen a second. Then there was the matter of the growth disease. He could eliminate hummed once faintly. "It's short-circulated their nervous systems for a while, absorbed the electric charges all intelligent beings cast," Irgi said aloud, glad at this chance to exercise his voice. "They won't be able to feel for some disease. Now he beheld the mighty salt mines where naked men swung huge picks at the crusted crystals, sweating and dying under a strange sun. Even these remnants of humanity festered with the growth. A tall, lean man in white looked out at him. His lips moved, and Irgi read their meaning. This man spoke to one named Emerson, commissioning him with a spaceship, reciting the need of radium, the dread of the plague. The thoughts of this Emerson were coming in clearer, as Irgi in sudden interest, flipped over different dials. The unspoken thoughts pouring into his brain through the screen continued. The words he did not understand, but the necessity for radium, and the danger of the growth disease he did. The pictures jumbled, grew chameleonesque— Irgi stared upward at a colossal figure graven in lucent white marble. Why, he had the power to make himself immortal! These creatures would but he could save it ! Opening the laboratory door, Irgi passed out and closed it behind him. It was the sweat of agony trickling down his forehead and over his eyes could not stand it he could not— It woke the others. They too, bellowed and screamed and sobbed, and their arms and legs writhed like wild things in a trap. "Got to get free," Emerson panted, straining against the wristbands. "That fiend," yelled Mussdorf. "That ten-eyed, octopus-legged, black-hearted spawn of a mismated monster did this to us. Damn him! it." "Maybe—maybe he's vivisecting us," moaned Nichols. "With rays or—or something—aagh! I can't stand it!" "Hang on, kid," gritted Emerson, fighting the straps. "I think it's "Nothing new. Remember me, Karl Mussdorf? I'm a convict, I am. A salt mine convict. I'd have done anything to get out of that boiling hell. I volunteered to go with you for the radium. Me and Gunn. Nichols doesn't count. He came on account of his wife and kids. We were the only two who'd come. Convicts, both of us."

<question>:
What caused the plague on earth?

<options>:
A It was a microbe from space travel
B It was a form of contagious cancer
C It was caused by cosmic rays that reached earth
D It was caused by radium

<answer>:

B