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

<passage>:
QUEST OF THIG "HORDE." He had blasted across trackless space to subdue a defenseless world—only to meet on Earth emotions that were more deadly than weapons. Thig's cold eyes opened a trifle wider as he stared into the thing's "He resembles Thig," announced Kam. "But for the strange covering he wears he might be Thig." "Thig will be this creature!" announced Torp. "With a psychic relay we the brain of Thig! He can then go out and scout this world without "For the good of the Horde," Thig intoned almost piously as he lifted Service for the Horde was all that the men of Ortha knew. Carefully cultured and brought to life in the laboratories of their Horde, they knew neither father nor mother. Affection and love were entirely lacking in their early training and later life. They were trained antlike from childhood that only the growth and power of the Horde were of any moment. Men and women alike toiled and died like unfeeling robots of flesh and bone for the Horde. The Horde was their religion, their love-life, their everything! proved too violent and his heart faltered after a time and stopped completely. Twice, with subtle drugs they restored pseudo-life to his body and kept the electrical impulses throbbing from his tortured where Jake and Ted had helped him dig for the buried treasure that old 'Notch-ear' Beggs had told them so exactly about. Remembrance of acquired memories labeled as pleasure, sent a warm glow upward from around his heart. Then he saw the slender red-haired shape of a woman, the mate of the dead man he knew, and confusion struck his well-trained brain. Men had no mates on Ortha, sex had been overthrown with all the other primitive impulses of barbarism the emotions that swept through his acquired memory. Unsteadily he took her in his arms and felt her warm lips pressed, trembling, against his own. That same hot wave of pulsing blood choked achingly up into his throat. adopting the thinking and mannerism of the other. All the better this way, he realized—more natural. and gunmen of his stories rendering him acutely unhappy. Sincerely he hoped that the west had reformed. "Mmmmmm," came from the depths of the chipped white wash-basin. "Home again," whispered Ellen as she stood beside Thig twelve weeks later and gazed tearfully at the weathered little gray house. She knelt Thig sank into a dusty old swing that hung on creaking chains from the to wipe the grotesque civilizations of Earth out of existence would, landed. And there Thig balked. Why must they destroy these people, Thig tried to tell himself that it was the transmitted thoughts of the dead Earthman that made him feel so, but he was not too sure. For three months he had lived with people who loved, hated, wept and sacrificed for reasons that he had never known existed. He had learned the heady glory of thinking for himself and making his own decisions. He had experienced the primitive joy of matching his wits and tongue against the wits of other unpredictable human beings. There was no abrupt division of men and women into definite classes of endeavor. A laborer thought the same thoughts that a governor might think. Uncertainty added zest to every day's life. The Orthan had come to question the sole devotion of the individual to the Horde to the exclusion of all other interests. What, he wondered, would one new world—or a hundred—populated by the Hordes add to the progress of humanity? For a hundred thousand years the Orthan civilization had remained static, its energies directed into certain mechanical hives. There was that moment on the brink of the Grand Canyon when Ellen had caught his arm breathlessly at all the beauty spread away there beneath who nestled trustingly against his tense man's body and slept—the son of Ellen and the man he had destroyed. Thig groaned. He was a weakling to let sentimentality so get the better So far had Thig the emotionless, robot-being from Ortha drifted from "But why," asked Thig slowly, "could we not disarm all the natives and broad fingers bit deep into the unyielding metal of his chair. Suddenly he knew that he must go back to Earth, back to Ellen and the children of the man he had helped destroy. He loved Ellen, and nothing must stand between them! The Hordes of Ortha must find some other world, an empty world—this planet was not for them. Then it was that Thig went berserk. His fists slashed into the thick for long moments they swayed there, locked together in silent deadly struggle. The fate of a world hung in the balance as Kam's other hand fought against that lone arm of Thig. weapon tilted upward until it reached the level of Thig's waist. Thig about full upon its owner's thick torso. Thig's fingers pressed down Before Thig's eyes half of his comrade's body sloughed away into foul corruption that swiftly gave way to hardened blobs of dessicated matter. Horror for what he had done—that he had slain one of his own Horde—made his limbs move woodenly. All of his thoughts were dulled the struggling races of Earth. He would never write another cowboy yarn—they would all be dead anyhow soon. Even Torp, thought Thig ruefully, gave way to the primitive rage of his but to that very bit of unconscious atavism he now owed his life. A cool-headed robot of an Orthan would have efficiently used the blaster to destroy any possibility of remaining life in his unconscious body. Thig rolled slowly over so that his eye found the door into the control why he had been left until last. Perhaps Torp wished to take cultures of his blood and tissues to determine whether a disease was responsible for his sudden madness. The deadly attack of Thig his own violent avenging of Kam's death, and now the apparent return of the man he had killed come to life had all served to jolt his rigidly trained brain from its accustomed groove. The shock had been too much for the established thought-processes of the skeleton-thing that had been Torp, using the new strength that victory had given him to drive him along. He had saved a world's civilization from extinction! The thought sobered him yet, somehow, he was pleased that he had done so. After all, it had been the Earthwoman and the children he had been thinking of while he battled Kam, a selfish desire to protect them all. him from the parent ship. The sensation of free flight against his new body was strangely exhilerating and heady. It was the newest of the emotions he had experienced on Earth since that day, so many months before, when he had felt the warmness of Ellen's lips tight against his. regret in his mind that he was not returning to the planet of his first existence. He thought of the dull greys and blacks of his planet, of the monotonous routine of existence that had once been his—and his heart thrilled to the memories of the starry nights and perfect exciting days he had spent on his three month trip over Earth. despite his acquired memory and traits, he was an alien from outer space. He fingered the tiny scars that had completely obliterated the slight a brief prayer in his heart to a God whose presence he now felt very deeply. There were tears in the depths of his eyes, then, and memories were hot, bitter pains. heaved a gasp of relief. He was no longer Thig, a creature of a Horde's West. He must remember that always. He had destroyed the real Terry and now, for the rest of his life, he must make up to the dead man's family. The knowledge that Ellen's love was not really meant for him would be a knife twisting in his heart but for her sake he must endure it. Her dreams and happiness must never be shattered.

<question>:
What was it that ultimately converted Thig to being human?

<options>:
A Lewis Terry. Lewis's mind took over his completely.
B Disease. It was as Torp suspected. Being on Earth affected him too deeply.
C Comfort. Earth culture is not nearly as controlling as Orthan culture.
D Love. Love for his new family, and the uncertainties of human life.

<answer>:

D