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

<passage>:
Grannie Annie, that waspish science-fiction writer, was in a jam again. What with red-spot fever, talking cockatoos and flagpole trees, I was running in circles—especially since Grannie became twins every now and then. entered the outer limits of the Baldric. Grannie Annie strode in the As we reached the first of those trees, Grannie came to a halt. was crazy. But Miss Flowers, known to her friends as Grannie Annie, Grannie Annie was the original research digger-upper, and when she persuade Miss Flowers not to attempt a trip into the Baldric." flagpole trees and a species of ornithoid resembling cockatoos. So far no one has crossed the Baldric without trouble." "What sort of trouble?" Grannie Annie had demanded. And when Antlers Park stuttered evasively, the old lady snorted, "Fiddlesticks, I never then abruptly I saw something else. A queer-looking bird squatted there in the sand, looking up at me. Silver in plumage, it resembled a parrot with a crest and yet it didn't. In some strange way the thing was a hideous caricature. "Look what I found," I yelled. "What I found," said the cockatoo in a very human voice. "Thunder, it talks," I said amazed. "Talks," repeated the bird, blinking its eyes. The cockatoo repeated my last statement again, then rose on its short legs, flapped its wings once and soared off into the sky. Xartal, the Martian illustrator, already had a notebook in his hands and was cockatoos and more flagpole trees. Above us, the great disc of Jupiter began to descend toward the horizon. And then all at once Grannie stopped again, this time at the top of a just crossed. "Billy-boy," she said to me in a strange voice, "look down there and tell me what you see." awe. The duplicate of myself was talking to the duplicate of Grannie Grannie shook her head. "Might be a form of mass hypnosis superinduced the sand seemed to grow more and more powdery. For some time I had fixed my gaze on a dot in the sky which I supposed to be a high-flying cockatoo. As that dot continued to move across the heavens in a single direction, I called Grannie's attention to it. "It's a kite," she nodded. "There should be a car attached to it somewhere." She offered no further explanation, but a quarter of an hour later as Grannie was shaking his hand vigorously and mumbling introductions. "I can't tell you how glad I am you're here, Grannie," he said. "If Grannie's eyes glittered. "Trouble with the mine laborers?" she "But surely you must have some idea of where they go," Grannie said. Baker lit a cigarette. "There's all kinds of rumors," he replied, "but none of them will hold water. By the way, there's a cockatoo eyrie ahead of us." I followed his gaze and saw a curious structure suspended between a rude circle of flagpole trees. A strange web-like formation of translucent gauzy material, it was. Fully two hundred cockatoos were perched upon it. They watched us with their mild eyes as we passed, but they didn't move. notebook out, sketching the room's interior. Grannie Annie remained Grannie Annie walked across to it and began to study its markings. Grannie nodded. "I think you and I and Xartal had better take a run up of the building. Grannie seized a light weight carry-case and began foreboding. Had I been a fool to let Grannie go? I thought of her, an It was a scene of a rapidly unfolding desert country as seen from the rear of a kite car. Directly behind the windscreen, backs turned to me, were Jimmy Baker, Grannie, and Xartal. It was as if I were standing directly behind them. "Sure." The operator turned another dial, and Grannie's falsetto voice posted of Grannie's movements. Then once more I was directly behind my friends, listening in on their conversation. The view through the windscreen showed an irregular array of flagpole trees, with the sky dotted by high-flying cockatoos. "There's an eyrie over there," Jimmy Baker was saying. "We might as well camp beside it." Ezra spoke over my shoulder. "He's doing scenes for Grannie's new Look at that damned nosy bird! " A silver cockatoo had alighted on the kite car and was surveying curiously Xartal's work. As each drawing was completed, the bird scanned it with rapt attention. Abruptly it flew to the top of the eyrie, where it seemed to be having a consultation with its bird companions. And then abruptly it happened. The cockatoos took off in mass flight. A group of Earth people suddenly materialized on the eyrie, talking and moving about as if it were the most natural thing in the world. With a shock I saw the likeness of myself I saw Ezra Karn and I saw the image of Jimmy Baker. The real Jimmy Baker stood next to Grannie, staring up at this incredible mirage. Grannie let out a whoop. "I've got it!" she said. "Those things we see up there are nothing more than mental images. They're Xartal's drawings!" "Don't you see," the lady continued. "Everything that Xartal put on paper has been seen by one or more of these cockatoos. The cockatoos are like Earth parrots all right, but not only have they the power powerful photographic impression of the object. That impression is then transmitted simultaneously in telepathic wavelengths to common foci. That eyrie might be likened to a cinema screen, receiving brain vibrations from a hundred different sources that blend into the light field to form what are apparently three-dimensional images." birds reconstruct images from the actual person. Why use drawings?" "Probably because the drawings are exaggerated in certain details and made a greater impression on their brains," Grannie replied. of Grannie Annie was bowing to the duplicate of Jimmy Baker, and the served a double purpose. It opened a shutter, and it rotated the lens slowly so that it played for a time on each of the sleeping men. Ezra Karn jabbed my elbow. "Grannie's coming back. I thought she'd be It was Grannie. As the car drew up alongside I saw her sitting in her Then, like a knife thrust, the truth struck me. "Ezra!" I yelled, swinging the car. "That wasn't Grannie! That was one of those damned cockatoo images. We've got to catch him." The other car was some distance ahead now. Park looked back and saw us with a steady powerful pull to the connecting wire. Park's vehicle appeared in our windscreen inches above Karn's head. the flagpole trees. I had to catch that car I told myself. Grannie but the triangular kite faltered. Taking advantage of Park's loss of "Grannie!" I yelled. "What're you doing here? Where's Mr. Baker?" "I see you've got Antlers Park. I'm glad of that. It saves me a lot of trouble." She took off her spectacles and wiped them on her sleeve. "Don't look so fuddled, Billy-boy. Come along, and I'll show you." Grannie Annie told her story during the long ride back to Shaft Four. Then suddenly becoming fearful of Grannie's prying, Antlers Park strove lens button. But Grannie only pretended to contract the plague. Park then attempted to outwit Ezra Karn and me by returning in Jimmy Baker's kite car with a cockatoo image of Grannie.

<question>:
Why does Grannie fool Billy as well when she rides away with Park?

<options>:
A She didn't want Billy to know where they were heading.
B She had to pretend she was replaced by a cockatoo, and make it convincing.
C She didn't want Antler to know about the cockatoo images and how they worked.
D She didn't. It was one of the cockatoo images.

<answer>:

D