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

<passage>:
the U.S. copyright on this publication was renewed.] "The outlaw ships are attacking!" Old Garmon Nash's harsh voice snapped like a thunderclap in the cramped rocket flyer's cabin. "Five or six of them. Cut the searchlights!" order. But here in the cavern world, thirty-seventh in the linked series of vast caves that underlie the waterless wastes of Mars, the reflected waves of sound were of little value. Distances were far too cramped—disaster might loom but a few hundred feet away. "Trapped us neatly," Rolf said through clenched teeth. "Tolled into their underground hideout by that water-runner we tried to capture. We can't escape, that's certain. They know these caverns better than.... We'll down some of them, though." "Right!" That was old Garmon Nash, his fellow patrolman aboard the Rolf swung the lax controls over hard as the bursts of fire revealed a In a slow sort of wonder Rolf felt the scrape of rock against metal, and then the screeching of air through the myriad rents in the cabin's meralloy walls grew to a mad whining wail. Down plunged the battered ship, downward ever downward. Somehow Rolf split open like a rotten squash, and Rolf felt himself being flung far outward through thick blackness. For an eternity it seemed he hung in the darkness before something smashed the breath and feeling from his nerveless body. With a last glimmer of sanity he knew Much later Rolf groaned with the pain of bruised muscles and tried to blasted the crashed ship, his practiced eyes told him, and Garmon Nash deep crevice. In the fading glow of the super-heated metal the vertical walls above mocked him. There could be no ascent from this natural prison-pit, and even if there were he could never hope to reach the surface forty miles and more overhead. The floors of the thirty-seven caves through which they had so carefully jetted were a splintered, creviced series of canyon-like wastes, and as he ascended the rarefied atmosphere of the higher levels would spell death. Rolf laughed. Without a pressure mask on the surface of Mars an caves there were no pressure domes for hundreds of miles. Here at He found the opening less than ten paces from the starting point, an endless plodding along that smooth-floored descending tunnel. "They may have found the sunken seas of Mars," thought Rolf as he moved it seemed to Rolf that he must be falling free through black dust, and he came to a stop. Deftly Rolf nested the Ten steps he took before an excited voice called out shrilly from the rocks ahead. Rolf's slitted gray eyes narrowed yet more and his hand "Down, Altha," a deeper voice rumbled from above, "it's one of the Enemy." Rolf threw up the mental block that was the inheritance from his grueling years of training on Earth Base. His instructors there "Sorry," said the tall man as Rolf sprang easily from the ground to Famous explorer you know. I was his assistant." "Sure." Rolf nodded. "Lost in equatorial wastelands—uh, about twenty years ago—2053, I believe." "Only we were not lost on the surface," explained Tanner, his booming "One," repeated Rolf slowly. "You mean there are more?" "Dozens of them," the older man's voice throbbed with helpless rage. beyond this first one, their floors flooded with water." Rolf felt new strength pump into his tired bruised muscles. Here lay they filed downward from the Barrier into the blackened desolation of Rolf watched the column of barbarically clad warriors file out upon the utterly shoulderless, and beneath their furry pelts the ripples of smooth-flowing muscles played rhythmically. There was a stench, a musky her narrow earless skull. And the skulls of rodents and men alike linked together into ghastly festoons about her heavy, short-legged litter. Men bore the litter, eight broad-shouldered red-haired men whose arms had been cut off at the shoulders and whose naked backs bore the weals off their retreat. After they have passed I will arouse the Outcasts who live here upon the Barrier. Though their blood is that of the two races mingled they hate the Furry Ones." Gone now was their chance for a surprise attack on the isolated canyons hideous scrawling battle-cry burst from their throats. Rolf's expoder rattled briefly like a high-speed sewing machine as he Tanner smashed an elbow into Rolf's side. "Retreat!" he gasped. "To the vaults beneath the Forbidden City," Mark Tanner cried. "None went bounding away along a shadowy crevice that plunged raggedly into Darkness thickened as they penetrated into the maze of the Barrier's glider riding the thermals back toward the Barrier. "She had warned the "The weasel heads won't follow us here?" asked Rolf. Rolf laughed. "Like the pleasure globes of the wealthy on Earth." a fortress for the few thousand aristocrats and slaves who escaped the surface wars. Rolf pushed up and outward with all the strength of his weary muscles. over the Barrier. The Furry Ones were struggling insect shapes below him, and he saw with a thrill that larger bodied warriors, whose bodies glinted with a dull bronze, were attacking them from the burnt-out had taken shelter, noting as he did so that the rocket flyer had landed him grin. He drove directly toward the grounded ship. With this rocket flyer he could escape from Lomihi, return through the thirty-seven momentarily. In that instant Rolf launched himself from the open They went down, Rolf swinging his fist like a hammer. He felt the Frog the guard's rifle expoder in his grasp the problem of escape from the inner caverns was solved. He would rescue the girl, stop at the Forbidden City for Mark Tanner, and blast off for the upper crust forty miles and more overhead. not blasted a vital spot in the man's body. The odds were evening, he thought triumphantly. There might be another outlaw somewhere out there in the badlands, but no more than that. The flyer was built to accommodate no more than five passengers and four was the usual number. He shifted his expoder to cover the opposite end crushed downward, breathless, his eyes glimpsing briefly the soiled greenish trousers of his attacker as they locked on either side of his neck, and then blackness engulfed him as a mighty sledge battered undisciplined men would have permitted to accumulate. Cautiously his head twisted until he could look forward toward the The cabin shifted with the weight of bodies moving from their seats. Rolf heard voices from a distance and the answering triumphant bawling "Fire!" There was panic in the outlaw's voice. Rolf came to his knees One of the men flung himself out the door, but the other reached for the extinguisher close at hand. His thoughts were on the oily smoke not on the prisoners, and so the impact of Rolf's horizontally propelled body drove the breath from his lungs before his hand could drop to his belted expoder. jolted upward toward the patrolman's vulnerable middle. But Rolf bored in, his own knotted hands pumping, and his trained body weaving instinctively aside from the crippling blows aimed at his body. For a moment they fought, coughing and choking from the thickening pall of the wreck in the upper cavern and the long trek afterward through the dark tunnels had sapped his strength, and now he felt victory slipping from his grasp. Rolf grinned up at her. "Need to?" he asked. all the time," she quipped. Then they were over the Barrier and Rolf saw the last of the beaten Rolf snorted. "Shorty," he said disgustedly as they landed, but his arm

<question>:
How many caves had Garmon and Rolf traveled through before their crash?

<options>:
A thirty seven
B forty seven
C thirty
D forty

<answer>:

A