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

<passage>:
I repeated it patiently. "But why?" he cried, sinking down into the chair before me. In an instant all the joy had gone out of him. I could not understand his suffering, but I could recognize it. "You yourself have said it," I told him. "I am a being of logic, just Then he cried suddenly, "But I am your friend, Robert!" then we must not go back. It was very simple, but I knew that he could reason had told me that he had to die. That was the end of it. A tear was trickling down my cheek. Young Peter Karson put the last black-print down and sighed with satisfaction. His dream was perfect laying the core, and then the metal giant itself would begin to grow, glittering, pulsing with each increment of power, until at last it lay stern—all the children of his brain. Out there, away from the muffling, distorting, damnable blanket of atmosphere, away from Earth's inexorable gravitational pull, would be Relief washed over him, leaving him breathless. He was horrified, of course, but only abstractedly. For the moment he could only be R. Stein, Secretary of the Council, who said in part: "The reason for this ... order must be apparent to all civilized we face the most momentous struggle in our history. We face an enemy superior to ourselves in every way . challenge, for there is no alternative. Not only our individual lives are threatened, but our existence as a race. We must, and will, destroy the Invaders!" Peter sank back in his chair, the full shock of it striking him for the mechanism to "Etaoin Shrdlu," principally because he hated double-talk. There were left only two blood-red, malignant monstrosities somehow defiling the air they floated in and below them, a pitiful huddle of men and women, but they wanted to be. Their bodies had been impossibly joined, fused together into a single obscene, floundering mass of helpless protoplasm. The thin moaning that went up from them was more horrible than any cry of agony. strangled voice. "Stay off the streets. Hide yourselves. Stay off the streets...." His voice droned on, but neither of them heard it. Lorelei buried her head on his chest, clutching at him desperately. "They have to," he told her grimly. "There will be panics and suicides, and they know it but they have to do it. This isn't like a war, where the noncombatants' morale has to be kept up. There aren't going to be any noncombatants, this time. Everybody in the world has to know about them, so that he can fight them—and then it may not be enough." The viewpoint of the teleo sender changed as the two red beings soared Then they faded slowly. It was impossible to say whether they had gone through the solid wall, or simply melted away. The man and woman clung together, waiting. There was a thick, oppressive silence, full of small rustlings and other faint sounds that were no longer normal. Then, very near, a man screamed in a high, inhuman voice. The screamed dwindled into a throaty gurgle and died, leaving silence again. Peter's lips were cold with sweat. Tiny nerves in his face and arms She was after him, clinging to his arms. "No, Peter! Don't go in there! Peter! " But he pushed her away again, woodenly, and stalked forward. range of vision. Peter forced himself forward another step. Little Harry Kanin, Lorelei's assistant, was crumpled in a corner, half supported by the broad base of an X-ray chamber. His face was flaccid and bloated. His The Invaders ignored Peter, staring expressionlessly down at Kanin. In a moment Peter realized what they were doing to him. He stood, The little man's body was sagging, ever so slowly, as if he were relaxing tiredly. His torso was telescoping, bit by bit his spread There was a scream in his throat that would not come out. He was beyond fear, beyond agony. He turned to the still-hovering monsters and said in a terrible voice, "Why? Why?" The scream was welling up. He fought it down and listened. " ... morofelcovisyanmamiwurlectaunntous. " He heard a faint sound behind him, and whirled. It was the first The scream came out then. Before he knew, even, that he could hold it back no longer, his mouth was wide open, his muscles tensed, his fingernails slicing his palms. It echoed with unbelievable volume in the room. It was a scream to split eardrums out of them. It had been nine and a half months, not three, and he'd been in a coma all that time. Lorelei, it seemed, had recovered much sooner. "But where is she?" Peter complained. "You still haven't explained why Arnold frowned. "All right," he said. "I guess you're strong enough to take it. She's underground, with the rest of the women and children, and a good two-thirds of the male population. That's where you'll go, "But why?" Peter whispered. Arnold's strong jaw knotted. "We're hiding," he said. "Everything else has failed." Peter couldn't think of anything to say. Dr. Arnold's voice went on It didn't take us long to find out we couldn't kill them. They didn't even take any notice of our attempts to do so, except once. That was when a squadron of the Police caught about fifty of them together at enough to take care of a quarter of the earth's population, the other three-quarters will be dead, or worse." "I wonder," Peter said shakily, "if I am strong enough to take it." Arnold laughed harshly. "You are. You've got to be. You're part of our last hope, you see." "Our last hope?" the left of the airlock— The Avenger . He stepped away now, and joined the group a little distance away, silently waiting. Lorelei said, "You can't do it. I won't let you! Peter—" "Darling," he began wearily. "Don't throw your life away! Give us time—there must be another way." "There's no other way," Peter said. He gripped her arms tightly, as if he could compel her to understand by the sheer pressure of his fingers. "They'll live, and we'll die, because they're a superior race. We're a million years too far back even to understand what they are or where they came from. Besides them, we're apes. There's only one answer." can't fight them , but a superman could. That's our only chance. Lorelei—darling—don't you see that?" She choked, "But why can't you take me along?" too. You'd be their murderer." Her sobs gradually died away. She straightened slowly until he no longer had to support her, but all the vitality and resilience was gone boys !" he slumped down before them and listlessly closed the contact of the visiplate. of the underground chamber, making sure that all the spectators had retired out of the way of the blast. Then his clawed fingers poised The days merged into weeks, then months, and finally, far out, The Avenger curved into an orbit and held it. The great motors died, and the silence pressed in about him. mature, and after weeks or years destroyed the monstrosities that came from the incubators. Time went by, meaninglessly. He ate when he was were searching for." His eyes glowed suddenly in their misshapen sockets. "You are. Your brain is as superior to mine as mine is to an anthropoid's. You solve instinctively problems that would take our mechanical computers hours can kill the Invaders, Robert."

<question>:
Why was Robert the only choice for returning to Earh?

<options>:
A He was the only changeling-child who grew to have no fear.
B He was the only changeling-child who had not been destroyed
C He was the only one will the powerfully strong talons that could defeat the Invaders
D He was the strongest of the group

<answer>:

B