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 I was running in circles—especially since Grannie became twins every now and then. time, and now as the immense disc of Jupiter flamed across the sky, entered the outer limits of the Baldric. Grannie Annie strode in the lead, her absurd long-skirted black dress looking as out of place in this desert as the trees. 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, had always been mildly crazy. If you haven't read her books, you've Lady of the Green Flames , Lady of the Runaway Planet , other works of science fiction. Blood-and-thunder as these books are, however, they have one redeeming feature—authenticity of background. Grannie Annie was the original research digger-upper, and when she laid the setting of a yarn on a star of the sixth magnitude, only a transportation-velocity of less than light could prevent her from visiting her "stage" in person. "What sort of trouble?" Grannie Annie had demanded. And when Antlers Park stuttered evasively, the old lady snorted, "Fiddlesticks, I never saw trouble yet that couldn't be explained. We leave in an hour." on foot with only the barest necessities in the way of equipment and supplies. 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. And then all at once Grannie stopped again, this time at the top of a "Billy-boy," she said to me in a strange voice, "look down there and I followed the direction of her hand and a shock went through me from head to foot. Down there, slowly toiling across the sand, advanced a party of four persons. In the lead was a little old lady in a black dress. Behind her strode a grizzled Earth man in a flop-brimmed hat, another Earth man, and a Martian. awe. The duplicate of myself was talking to the duplicate of Grannie Annie, and she was replying in the most natural way. Grannie shook her head. "Might be a form of mass hypnosis superinduced heavens in a single direction, I called Grannie's attention to it. She offered no further explanation, but a quarter of an hour later as Grannie was shaking his hand vigorously and mumbling introductions. he was tall and lean, with pleasant blue eyes which even his sand goggles could not conceal. "I can't tell you how glad I am you're here, Grannie," he said. "If anybody can help me, you can." Grannie's eyes glittered. "Trouble with the mine laborers?" she Jimmy Baker nodded. He told his story over the roar of the wind as we excellent living conditions with a vacation on Callisto every year. Up until a short time ago most of them were in excellent health and "Red Spot Fever?" Grannie looked at him curiously. Jimmy Baker nodded. "The first symptoms are a tendency to garrulousness "But surely you must have some idea of where they go," Grannie said. . As Jimmy Baker led the way up the inclined ramp, Baker dropped his cigarette and ground his heel on it savagely. notebook out, sketching the room's interior. Grannie Annie remained standing. Presently the old lady walked across to the desk and helped herself to "There must be ways of stopping this," she said. "Have you called in any physicians? Why don't you call an enforced vacation and send the men away until the plague has died down?" threw off the switch. 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 There was no refusing her. Jimmy Baker led the way down to a lower level where a huge laboratory and experimental shop ran the length of the building. Grannie seized a light weight carry-case and began The kite car was brought out again, and the old woman, Baker and the Not until they had vanished in the desert haze did I sense the loneliness of this outpost. With that loneliness came a sudden sense of foreboding. Had I been a fool to let Grannie go? I thought of her, an old woman who should be in a rocking chair, knitting socks. If anything happened to Annabella C. Flowers, I would never forgive myself and neither would her millions of readers. were Jimmy Baker, Grannie, and Xartal. It was as if I were standing "It's Mr. Baker's own invention," the operator said. "An improvement on "Sure." The operator turned another dial, and Grannie's falsetto voice The cloud of anxiety which had wrapped itself about me disappeared somewhat as I viewed this device. At least I could now keep myself posted of Grannie's movements. "Miss Flowers left with Mr. Baker for Shaft Four," I said. "There's it, I might drive over to Shaft Four and give Jimmy Baker the formula. "There's an eyrie over there," Jimmy Baker was saying. "We might as of the car and began making camp. Xartal remained in his seat. He was moving about as if it were the most natural thing in the world. With a shock I saw the likeness of myself Jimmy Baker stood next to Grannie, staring up at this made a greater impression on their brains," Grannie replied. of Grannie Annie was bowing to the duplicate of Jimmy Baker, and the "That explains something at any rate," the old prospector said. "But attacked by the strange malady. Reading them over, I was struck by one detail. Each patient had I seized it and pulled it loose, I felt the hum of tiny clock work. I slid the metal button in my pocket and left the barracks at a run. I stared with open eyes. Jimmy Baker no longer was in the car, nor Ezra Karn jabbed my elbow. "Grannie's coming back. I thought she'd be getting sick of this blamed moon." It didn't make sense. In all the years I'd known Annabella C. Flowers, never yet had I seen her desert a case until she had woven the clues and facts to a logical conclusion. another car approaching. It was Grannie. As the car drew up alongside I saw her sitting in her "We left the others at the mine. Miss Flowers is going back with me to "Ezra!" I yelled, swinging the car. "That wasn't Grannie! the flagpole trees. I had to catch that car I told myself. Grannie Annie's very life might be at stake, not to mention the lives of thing he could do. He shut off power, and the two cars coasted to a "What have you done with Miss Flowers?" I demanded. with an exclamation of astonishment. There was a huge chair-shaped rock there, and seated upon it was Grannie Annie. She had a tablet in her hands, and she was writing. "Grannie!" I yelled. "What're you doing here? Where's Mr. Baker?" "Don't look so fuddled, Billy-boy. Come along, and I'll show you." upon the marching men were Jimmy Baker and Xartal, the Martian. reached Shaft Four." Grannie Annie told her story during the long ride back to Shaft Four. We drove slowly, keeping the line of marching Larynx miners always ahead of us. Jimmy Baker had struck a new big lode of Acoustix, a lode which if Then suddenly becoming fearful of Grannie's prying, Antlers Park strove He did head her off and managed to lure her and Baker and Xartal into 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>:
Although Billy-boy questioned his decision of letting Grannie Annie leave with Baker in the kit car, what put his mind at ease?

<options>:
A The car and its passengers were safe from the Red Spot Fever
B The kite car was protected by the strange birds.
C The invention by Baker allowed them to watch the movements of the car and its passengers
D She was a strong woman and capable of taking care of herself.

<answer>:

C