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

<passage>:
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 great cliffs and the hills that were his home. His handsome face broadened into a smile and he quickened his pace to a trot. There was no need for caution now. The dangers on the plain were 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 him swiftly toward the distant hills. His movements were graceful, easy, as the loping of Shee, the great cat. Then, suddenly, he faltered in his stride. He stopped running and, shielding his eyes from the sun's glare, stared ahead. There was a figure running toward him. And behind that first figure, a second gave chase. For a long moment Ro studied the approaching creatures. Then he gasped in surprise. The pursued was a young woman, a woman he knew. Na! The pursuer was a squat, ugly rat man, one of the vicious Oan who lived in the cliffs. he searched the ground with his eyes. When he found what he sought—a round rock that would fit his palm—he stooped, and snatching up the missile, he ran forward. At great speed, he closed the gap between him and the approaching ribs and backbone cracked under the blow. He was dead before he struck the ground. With hardly a glance at his fallen foe, Ro ran on to meet the girl. She fell into his arms and pressed her cheek to his bare shoulder. Her dark Na lowered her eyes. "I was caught in the forest below the cliffs. The Oan spied me and I ran. The chase was long and tiring. I was almost ready to drop when you appeared." "You were alone in the woods!" Ro exclaimed. "Since when do the women of our tribe travel from the cliffs alone?" "Since a long time," she answered sadly. Then she cried. And between sobs she spoke: "Many weeks ago a great noise came out of the sky. We ran to the mouths 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 hands and one beneath their armpits, they climbed down to battle or 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. Na smiled. Ro was angry, but anger did not make him blind. He would make a good mate. The sun was setting when the two Martians reached the cliffs. Below them was the valley in which lay the metal sphere. Ro could see it on a mountain peak. "You say they came from a place called Earth?" Ro asked Na in wonder. "They traveled through space in their 'ship,'" Na answered. "They 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. he kissed her, as was the custom of his tribe when a man took a wife. Without another word he disappeared over the edge of the cliff. They had already made plans for their next meeting. There was no need for a prolonged farewell. They would be together soon—on the far side of the to hold to in the almost smooth wall. His toes seemed to have eyes to pierce the darkness in finding footholds. The climb was long and dangerous. Ro's skin glistened with sweat. 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 he rested at the bottom. Feeling his way cautiously, he moved toward the camp. He could sense 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 His breathing was heavy as he struggled with the knots. But finally the golden-haired girl was free. easily as each came free and he started on the next. 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. them and Oan camp grew. Ro increased his pace when silence was no longer necessary. The four white people stumbled ahead more quickly. "We journey out of the valley and around the face of the cliffs," Ro told them. "After a short while, we will meet Na." "Who is Na?" asked the girl. The white girl was silent. They traveled quite a distance without communicating. Each was busy with his own thoughts. He stopped walking and stared around him for a landmark. They had traveled far along the foot of the cliff. According to the plan Na 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 under the weight of a burden. It was a rat man, and slung across his shoulders was a girl. Ro's body tensed and quivered. A low growl issued from deep in his throat. He charged forward. The Oan saw him coming and straightened, allowing the girl to fall. He and lay still. Ro dismounted the limp body. His face wore a wildly triumphant expression. It changed as he remembered the girl. He ran to her side. Na was just opening her eyes. She stared around her fearfully, then relief. Na turned her head and saw the body of the rat man. She shuddered. "I was coming down the side of the mountain," she said. "I saw him standing at the foot. The shadows were deceiving. I thought it was you. It wasn't until too late that I discovered my mistake." Ro gathered the girl in his arms. He spoke softly to her to help her forget. When she had recovered from her shock, the small group traveled on. Ro led them about a mile further along the base of the cliff, then up, to a cleverly concealed cave. "We will stay here," he told the others, "until we are ready to attack One was lean and determined, the other, equally determined, but stouter and less impressive. Ro then centered his attention on the girl. Her Ro awakened with the dawn. He was startled to find that Na had left his side. He rose quickly and strode to the mouth of the cave. Na met him at the entrance. She was returning from a clump of trees a short distance away. Her arms were loaded with Manno, the fruit of Mars, and clusters of wild berries and grapes. burden. The others in the cave awakened. Ro noticed that Charlotte had slept He repeated his plan to the others. "But they'll kill her," gasped Charlotte. Ro laughed. "Do you think I will let her go alone? I will be close by. Na can lead the rat men through a narrow part of the valley. I will be above on the professor." valley. It was about a hundred yards long and twenty feet wide. The walls of the cliff rose almost straight up on both sides. "We leave you here," said Ro to the professor. "Na will lead you to the sphere. She will remain hidden until you have circled away from her. will try some strategy of their own." Carlson seemed to come out of a trance. He swung around to trail Ro up the sloping part of the mountain. They climbed in silence. Once Ro stopped to look down into the valley. But Na and the others were gone. He felt a pang of regret as he turned to move upward. When they had reached the top, he and Carlson set to work piling rocks and boulders at the edge of the cliff. They chose the point directly over the narrowest part of the valley. If all went well, the Oan would be trapped. They would die under a hailstorm of rock. "You would have liked a more tender goodbye with Charlotte," Ro said to

<question>:
Why did Na not meet the party on time?

<options>:
A She accidentally walked up to an Oan
B She went to find the white people
C She stayed on the cliff
D She was coming down the side of the mountain

<answer>:

A