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

<passage>:
times he had seen fellow Martians die by the razor fangs of Gin, the swamp snake. Their clear red skin had become blotched and purple, their eyeballs popped, their faces swollen by the poison that raced through their veins. And Ro had seen the bones of luckless men vomited from the mouths of the Droo, the cannibal plants. And others there had been, some friends of his, who had become game for beasts of prey, or been swallowed by hungry, sucking pools of quicksand. No, the jungles of Mars were not to be taken casually, no matter how light in heart one thatched huts, the strange people who lived in these huts instead of in caves, and wore coverings on their feet and shining rings in their ears. And having quenched his curiosity about these people and their and all his brothers and sisters to sit round a fire with them at the entrance to their cave and tell of the wondrous places he'd visited. And, most of all, he wanted to see Na, graceful, dark eyed Na, whose few. The sun beat down on his bare head and back. His red skin glistened. His thick black hair shone healthily. Mile after mile fell behind him. His long, well muscled legs carried furry face and twitching tail. The Oan, however, was too intent The Oan squealed in terror and tried to swerve from his course. The her gaze, as was the custom among the men of his tribe when dealing with women but he smiled instead. Na lowered her eyes. "I was caught in the forest below the cliffs. The Oan spied me and I landing in the valley below. Many colored fire spat from one end of it. "The men of our tribe snatched up stones, and holding one in their white as the foam on water, and clothed in strange garb from the neck down, even to coverings on their feet. They made signs of peace—with one hand only, for they carried weapons of a sort in the other. And the men of our tribe made the same one-handed sign of peace, for they would not risk dropping their woman with golden hair, and the other, a man of age, with hair like silver frost. "There was a great feast then, and our men showed their skill at throwing. Then the white men displayed the power of their strange weapons by pointing them at a tree and causing flame to leap forth to burn the wood in two. We were indeed glad they came in peace. "That night we asked them to sleep with us in the caves, but they made camp in the valley instead. The darkness passed swiftly and silently, and with the dawn we left our caves to rejoin our new friends. But everywhere a red man showed himself, he cried out and died by the flame from the white men's weapons. "I looked into the valley and saw hundreds of Oan. They had captured our friends in the night and were using their weapons to attack us. There was a one-sided battle that lasted three days. Finally, under cover of night, we were forced to leave the caves. One by one we went, and those of us who lived still travel alone." Surely he didn't fall to the Oan?" "He had no chance to fight," Na answered. "Two of your brothers died with him on that first morning." Ro squared his shoulders and set his jaw. He wiped a hint of tears from his eyes. "They shall pay," he murmured, and started off toward the cliffs again. Na trailed behind him. Her face was grave with concern. "They are very many," she said. "Then there will be more to kill," answered Ro without turning. "They have the weapons of the white ones." "And the white ones, as well. They probably keep them alive to repair the weapons if they become useless. But when I have slain a few Oan, I to place. There were no fires, for the Oan were more beast than man and feared flame called themselves an expedition." Ro was silent then. In a short time it would be dark enough to go down into the valley. When he had rescued the white ones, he would learn more about them. He turned away from the valley to study Na. She was very beautiful. Her dark eyes seemed to sparkle and her hair shone in the twilight. He understood why she had crept into his dreams. The darkness settled quickly. Soon Ro could barely make out the girl's good weight and would make short work of any Oan who was foolish enough He had lived in the cliffs all his life, and had made many perilous climbs, but never one on so dark a night. It seemed an eternity before the presence of many Oan close by. The hair at the base of his neck prickled. He prayed he wouldn't be seen. An alarm now would spoil his Suddenly he halted. A dim figure approached. It was one of the Oan, a guard. He was coming straight at Ro. The young Martian shrank back. "The rat men have eyes to cut the night." It was a memory of his mother's voice. She had spoken those words when he was a child, to keep him from straying too far. The Oan was only a few feet away now, but his eyes were not cutting the night. Ro could see his large ears, hear his twitching tail. In a moment the beast would stumble over him. clearing without making a sound. Strewn on the ground were shapeless heaps. They would be the slumbering rat men. Ro suppressed an urge to spring amongst them and slay them as they slept. He lay flat on his stomach and inched his way ahead. It was slow work, but safer. When a sound reached his ears he drew himself together and feigned sleep. In the dusk he appeared no different than the others. His chest was scratched in a thousand places when he reached the far side, but he felt no pain. His heart was singing within him. His job When they were ready, Ro signaled the four white people to follow him. They rose quietly and trailed him into the woods. The girl whispered something to one of the men. Ro turned and glared at her through the shadows. The progress they made was slow, but gradually the distance between "With your help I will avenge the death of my father and brothers and the men of my tribe." He stopped walking and stared around him for a landmark. They had should have met them minutes ago. Then he gave a glad cry. Squinting ahead he saw an approaching figure. It was—His cry took on a note of alarm. The figure was bent low throat. He charged forward. The Oan saw him coming and straightened, allowing the girl to fall. He set his twisted legs and bared his fangs. The fur on his back stood out Over and over they rolled. The Oan clawed urgently at the Martian's the Oan." He sat in a corner of the cave and leaned back against the wall. His eyes were half shut and he pretended to doze. Actually he was studying the white ones. The man with the silver hair seemed very old and weak, but very wise. pure white. They were handsome, Ro thought, in a barbaric sort of way. One was lean and determined, the other, equally determined, but stouter table if you wander off. Your next meeting with the Oan may not be so The others in the cave awakened. Ro noticed that Charlotte had slept beside Carlson, but moved away shyly now that it was daylight. He noticed, too, that Grimm was seeing the same thing and seemed annoyed. "The Oan are cowards," Ro answered. "They are brave only because they than the Oan." "Perhaps the attraction you seem to hold for the Oan can be put to good use," he said aloud. "The sphere is a distance away from the Oan He repeated his plan to the others. "But they'll kill her," gasped Charlotte. "She will be a woman alone," said Ro. "The Oan prefer to capture women "This is no time for fighting," he said. "When the Oan are defeated you "Come on," Ro said. "If we spend the rest of the morning here, the Oan over the narrowest part of the valley. If all went well, the Oan would be trapped. They would die under a hailstorm of rock.

<question>:
What is the Oans' unusual advantage?

<options>:
A They have the human's fire weapons.
B They emit flames.
C The strength of their arms.
D Their eyes cut the night.

<answer>:

A