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

<passage>:
Planet Stories Summer 1944. Extensive research did not uncover any evidence that the U.S. copyright on this publication was renewed.] He heard the star-port grind open, and the movement of the metal claws groping into space, and then the star-port closed. feeling all tight and wild inside himself. It went on for days. Moving the ship. Opening the star-port. Extending the retriever claw. Plucking some poor forth from Earth to nowhere. You came out empty and you went back full-cargoed with a lot of warriors who didn't laugh or talk or smoke, who just lay on their shelves, all one hundred of them, waiting for a into a floor incinerator mouth. Back to Earth. Then spin around and shoot right out again in the trail of the war-rockets that blasted one another in galactic fury, to sidle up behind gutted wrecks of ships, salvaging any bodies still intact after the conflict. for action. This would be his last trip, or he'd know the reason why! "Sam!" shelves. Burnett stared at the tabled bodies as if they would leap to life, even while preservative was being pumped into their veins. "Sam! On the double! Up the rungs!" Burnett closed his eyes and said a couple of words, firmly. Nothing was All the color is ahead of you. The drive of orange rocket traces across stars, the whamming of steel-nosed bombs into elusive targets, the titanic explosions and breathless pursuits, the flags and the excited You come along when space has settled back, when the vacuum has stopped trembling from unleashed forces between worlds. You come along in the you don't hear anything in space but your own heart kicking your ribs. You see bodies, each in its own terrific orbit, given impetus by grinding collisions, tossed from mother ships and dancing head over suits, mouths open for air that had never been there in a hundred billion centuries. And they kept dancing without music until you extended the retriever-claw and culled them into the air-lock. all too quickly with men who had once loved laughing. You wondered who all the men were and who the next ones would be. with the body black. "Good Lord, Sam, do you know who this is?" Burnett scowled uneasily and said no. right?" "Don't say it calm, Sam. Say it big. Say it big! If Lethla is here in space, then Kriere's not far away from him!" What the hell. He was tired. Talk about bodies and rulers to someone "Look, Rice, you're new at this game. I've been at it ever since the Venus-Earth mess started. It's been see-sawing back and forth since the day you played hookey in the tenth grade, and I've been in the thick of it. When there's nothing left but seared memories, I'll be prowling green Earth. Grisly, yes, but it's routine. "As for Kriere—if he's anywhere around, he's smart. Every precaution is taken to protect that one." battle-cuiser to go against him?" swept out past Earth in a new war concerning Io. That's out, Rice." Rice stood about three inches below Sam Burnett's six-foot-one. Jaw hard and determined, he stared at Sam, a funny light in his eyes. His bloated and crushed by space pressures and heat-blasts. Fine lads who start out smiling and get the smile burned off down to the bone—" heart waiting warm and heavy at the base of his throat. "This is my last cargo, Rice. I can't take it any longer. And I don't care much how I go back to earth. This Venusian here—what's his name? Lethla. He's number ninety-eight. Shove me into shelf ninety-nine beside him and get the hell home. That's how I feel!" inserted, hidden in the uniform, ending in thin globules of oxygen. He spoke. Triumph warmed his crystal-thin voice. "That's how I did it, Earthman." "Glassite!" said Rice. "A face-moulded mask of glassite!" Lethla nodded. His milk-blue eyes dilated. "Very marvelously pared to as you saw it, outside the ship, floating in the void, not discernible at all." Prickles of sweat appeared on Rice's face. He swore at the Venusian and the Venusian laughed like some sort of stringed instrument, high and quick. Burnett laughed, too. Ironically. "First time in years a man ever came metal and glass and He smiled. "That's better. Now. We can talk—" Rice said it, slow: "Interplanetary law declares it straight, Lethla! Get out! Only dead men belong here." Lethla's gun grip tightened. "More talk of that nature, and only dead lidded, listening to the two of them as if they were a radio drama. Lethla's voice came next: "Rather unfortunately, yes. He's still alive, heading toward Venus at an orbital velocity of two thousand m.p.h., wearing one of these air-chrysali. Enough air for two more hours. Our flag ship was attacked unexpectedly yesterday near Mars. We were forced to take to the life-boats, scattering, Kriere and I in one, the others sacrificing their lives to cover our escape. We were lucky. We got through the Earth cordon unseen. But luck can't last forever. "We saw your morgue ship an hour ago. It's a long, long way to Venus. We were running out of fuel, food, water. Radio was broken. Capture was certain. You were coming our way we took the chance. We set a small time-bomb to destroy the life-rocket, and cast off, wearing our trick anyone. We knew you wouldn't know we were alive until it was too late and we controlled your ship. We knew you picked up all bodies for brief exams, returning alien corpses to space later." Rice's voice was sullen. "A set-up for you, huh? Traveling under the protection of the Purple Cross you can get your damned All-Mighty safe to Venus." Lethla bowed slightly. "Who would suspect a Morgue Rocket of providing safe hiding for precious Venusian cargo?" "Precious is the word for you, brother!" said Rice. "Enough!" Lethla moved his gun several inches. "Accelerate toward Venus, mote-detectors wide open. Kriere must be picked up— now! " Rice didn't move. Burnett moved first, feeling alive for the first time slow pace. Burnett set his teeth together, bone against bone. Help Kriere escape? See him safely to Venus, and then be freed? Sounded easy, wouldn't be hard. Venusians weren't blind with malice. Rice and he could come out alive if they cooperated. "Cut power! We don't want to burn him!" searching. Kriere, then, had to be taken aboard. After that— Kriere, the All-Mighty. At whose behest all space had quivered like was too much silence, and his voice sounded guilty standing up alone in the center of that silence. "Take controls, Rice. I'll manipulate the star-port." why— was about to end a ten-years' war. There was only one way of drawing Lethla off guard, and it had to be fast. it had done a thousand times before but for the first time it was a from space. claws come inside, and the star-port grind shut. Out of the red darkness, Rice's voice came and then he could see Rice's them out: "Rice?" "Yeah, Sam?" this rocket, and not once come back without a bunch of the kids who want to sleep easy on the good green earth. Not right to be going back any way—but—the way—we used to—"

<question>:
Why are Earth and Venus at war?

<options>:
A To maintain control of the solar system
B It is not revealed
C Venusians tried to colonize Earth
D Earth provoked the Venusians

<answer>:

B