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

<passage>:
cautious advance of three awed space-scouters. An hour later they surfaced about two hundred yards away from the Planet Stories Summer 1955. Ahead of them were the other two scoutships from the mother ship. Extensive research did not uncover any evidence that standing by the scoutships, and at the edge of the city, began to run edge of the city. Behind them the black pile rose, the dome of force occurred, and he and his two companions sat and stared in awed silence at the city a quarter-mile away. barren earth began ... and he remembered observing, even before they a graceful movement of hand and arm he indicated the waiting city. city. Malignant. He wondered, again, what beings would choose to build a city—even a city like this one—in such surroundings. The men from the ship knew only the surface facts about this waiting geometric discovery. Theirs was the eleventh inter-planetary flight, and the previous ten, in the time allowed them for exploration while this planet was still close enough to their own to permit a safe return in their ships, had not spotted the city. But the eleventh expedition had, an hour ago, with just thirteen hours left during which a return flight could be safely started. So far as was known, this was the only city on the planet—the planet without any life at all, save tiny mosses, for a million years or more. And no matter which direction from Wass murmured, "Let us hope they aren't immortal." Wass watched him, and then shoved aside more sand, several feet away. Martin shrugged. "Clear around the city? I'd like to know what it cautiously across five intersections. And they stood in a square surrounded by the tallest buildings in the city. "If we don't hurry up and get through this place and back to the ship, we're very likely to find out." looked back along the straight, metal street they'd walked on, and past lay ... and he thought everything outside the city seemed, somehow, He straightened his shoulders. The city was alien, of course, and that explained most of it ... most of it. But he felt the black city was something familiar, yet twisted and distorted. "Well," Wass said, his nose wrinkling a bit, "now that we're here...." "Pictures," Martin decided. "We have twelve hours. We'll start here. What's the matter, Wass?" There was a pause. Then Wass, defensively—"It's almost as if the city Parallel evolution on two inner planets of the same system? Somewhere, heavier gravity, remembered the inhabitants of the city vanished before be all around us." He was silent for a time, exploring the consequences this?" He shook his head angrily, saying, "Judging by reports of the rest of the planet, it must have been horribly radioactive at one time. All of alien-made, anyhow. Perhaps they had a war." Rodney interrupted, "There hasn't been enough radiation around here for hundreds of thousands of years to activate such a screen." Wass said coldly, "He's right, Martin." cover the city." buildings surrounding the square. The corridor inside was dim and plain, and he switched on his flashlight, the other two immediately following his example. The walls and the rounded ceiling of the corridor were of the same dull metal as the buildings' facades, and the streets. There were a multitude of doors and arches set into come to associate with the city builders. The three torches, shining Martin shrugged. "The whole city's no more than a machine, apparently." "Another assumption," Wass said. "We have done nothing but make assumptions ever since we got here." Rodney turned. "But—" "No. Wass, how much time have we?" "The ship leaves in eleven hours." "Eleven hours," Rodney repeated. "Eleven hours!" He reached out for the switch again. Martin swore, stepped forward, pulled him back roughly. "We have to find out what all this stuff's for!" "We've got to—" "No!" Then, more quietly—"We still have eleven hours to find a way out." "Ten hours and forty-five minutes," Wass disagreed softly. "Minus the time it takes us to get to the lifeboat, fly to the ship, land, stow it, get ourselves aboard, and get the big ship away from the planet. "You too, Wass?" "Up to the point of accuracy, yes." be at least half-a-dozen emergency exits around the city." Rodney said, "To search every building next to the dome clean around the city would take years." leading to them. Up here there are too many roads." "Have you a better idea?" Wass ignored that, as Martin hoped he would. He said slowly, "That on them. Wass turned his light parallel with the floor, and then moved slowly in a circle. "No supports. No supports anywhere. What keeps all that up there?" "No, no," Martin answered impatiently, "not just here. I mean the whole city." thought, paralleled the street above. And Rodney and Wass followed him three lights, past openings in the occasional high metal partitions, They began to retrace their steps along the metal street, back past surface level, how the city itself looked when they were landing, and then when they were walking toward it. The dream was gone again for But—The only city, so far as anyone knew, on the first planet they'd ever explored. And it had to be like this. Nightmares, Wass said, and some point twisted away from their evolutionary spiral, plagued by a the combined light of their torches would reach. Martin thought of the dark, convoluted land outside the city. If they find a way out of here." He started up the ramp. "Besides, we've no super-swiftness at the air valves and joints of their suits "—only the take off. Let's search awhile first. Let this be a last resort." Postpone and postpone until it's too late, and the ship leaves without us and we're stranded here to eat seeds and gradually dehydrate ourselves and God only knows what else and—" He reached out convulsively and yanked a switch. looking back. "It got in and out of the city some way. Perhaps we can picking out shadowy, geometrical shapes, duplicates of the ones on the present level. "We'll find out," he said, "how many there are." Eleven levels later Rodney asked, "How much time have we now?" "Seven hours," Wass said quietly, "until take-off." "One more level," Martin said, ignoring the reference to time. "I ... think it's the last." artificial light on the bottom level of the alien city. "This is different," Wass said. "Built-in traps—" "They had a war," Martin said. know?" Wass turned, too, persistent. "But the planet was through with them." "In a minute," Martin said, too irritably, "we'll have a sentient "We'll disperse and search carefully," Martin said. "I wonder what the pattern was." "... The reservoirs, Wass. The pattern will still be here for later expeditions to study. So will we if we don't find a way to get out." Their radios recorded Rodney's gasp. Then—"Martin! Martin! I think The three men, clad in their suits and helmets, grouped around the obscuring the dimly seen backdrop of geometrical processions of strange sank into the dust. "Not me," the answer came back quickly. "You two fools go your way, I'll go mine." "Wass!" and swirled about them until the purifying systems in their suits were "Of course," Martin growled. There was silence again, the silence of almost-exhausted determination. without number. Then Wass broke his silence, taunting. "The ship leaves in two hours, Martin. Two hours. Hear me, Rodney?" Martin pulled his left foot from the sand and growled deep in his throat. Ahead, through the confusing patterns of the sparkling dust, "I've been trying to get you," Rodney said, frantically. "Why didn't

<question>:
How many other expeditions ventured to the planet without noticing the city?

<options>:
A 11
B 10
C 0
D 7

<answer>:

B