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

<passage>:
Tr'en were an efficient people. All the preliminary reports had agreed on that their efficiency, as a matter of fact, was what had made Korvin's arrival a necessity. They were well into the atomic era, and the ordinary course of events, an invitation to join the Comity of Planets. An invitation, the Comity was sure, which the Tr'en would not accept. Korvin stretched out on the cell's single bunk, a rigid affair which that the Tr'en had seen fit to give him a pack of cards, or a book, or even a folder of tourist pictures. The Wonders of Tr'en, according to In any decently-run jail, he told himself with indignation, there would at least have been other prisoners to talk to. But on Tr'en Korvin was all alone. True, every night the guards came in and gave him a concentrated lesson in the local language, but Korvin failed to get much pleasure As he reached this dismal conclusion, the cell door opened. Korvin got up off the bunk in a hurry and spun around to face his visitor. The Tr'en was tall, and slightly green. He looked, as all the Tr'en did, vaguely humanoid—that is, if you don't bother to examine him closely. Life in the universe appeared to Korvin didn't really didn't care about it it was none of his business. The Tr'en regarded him narrowly through catlike pupils. "You are Korvin," he said. It was a ritual, Korvin had learned. "You are of the Tr'en," he replied. The green being nodded. the door behind him. Korvin thought of jumping the Tr'en, but decided quickly against it. He was a captive, and it was unwise to assume that there might be almost anything else hidden and ready to fire on him. "What do you want with me?" Korvin said. The Tr'en speech—apparently there was only one language on the planet—was stiff and slightly awkward, but easily enough learned under drug hypnosis Korvin sighed. "What are you doing here, then?" he asked. As to get the hang of, Korvin told himself bitterly. He thought for a pointed. Korvin stared back impassively. "I have been ordered to come you." It wasn't quite "talk" that was a general word in the Tr'en language, and Didyak had used a specific meaning, roughly: "gain information reference. "Why did the Ruler not come to me?" Korvin asked. Korvin shrugged, sighed and smoothed back his hair. "I obey the But Korvin meant exactly what he'd said. He was going to obey the commands of the Ruler of the Tr'en—and remove the Tr'en threat from the rest of the galaxy forever. That, after all, was his job. contrast of the Tr'en themselves were figured in. The Ruler himself, a Tr'en over seven feet tall and correspondingly broad, sat in the great chair, his four fingers tapping gently on the table near him, staring at Korvin and his guards. The guards stood on Korvin wasn't attempting to escape. He wasn't pleading with the Ruler. He wasn't defying the Ruler, either. He was just answering questions. The Tr'en liked to have everything clear. They were a logical race. The Ruler had started with Korvin's race, his name, his sex—if Korvin shrugged. "Some are over eight feet tall," he said, "and others under four feet." He used the Tr'en measurement scale, of course it didn't seem necessary, though, to mention that both extremes of height Korvin nodded hurriedly. "Our race is more ... more approximate," he "You will answer my questions," the Ruler said, "with exactitude." He Korvin looked around and saw it coming through the door, pushed by two straps. It was obviously a form of lie-detector—and Korvin felt The Tr'en, under other circumstances, would have been a valuable addition to the Comity of Nations. Being what they were, though, they could only be a menace. And Korvin's appreciation of the size of that menace was growing hourly. Korvin swallowed again. The test hadn't really seemed extensive enough to him. But, after all, the Tr'en knew their business, better than anyone else could know it. They had the technique and the logic and the training. The Ruler was frowning at him. Korvin did his best to look receptive. Korvin looked sober. "Yes," he said. Korvin decided to throw his first spoke into the wheel. "Staying "I have told the truth," Korvin said. Korvin shrugged. "I replied to your question," he said. "I did not Ruler," he said at last, in an approximation of his usual one. "But the Ruler will not be confused. We have experts in matters of logic"—the Tr'en word seemed to mean right-saying —"who will advise Korvin's guards were standing around doing nothing of importance now The Ruler looked down at Korvin. "You will find that you cannot trick Korvin The experts in logic arrived shortly, and in no uncertain terms Korvin the secretary of the club whose members were secretaries, Achilles and the tortoise, and all the other lovely paradox-models scattered around were so much primer material for the Tr'en. "They can be treated mathematically," one of the experts, a small emerald-green being, told Korvin thinly. "Of course, you would not understand the mathematics. "Naturally," Korvin said in a friendly tone. The expert frowned horribly, showing all of his teeth. Korvin did his "To answer your questions, truthfully and logically," Korvin said. Korvin was very glad that wasn't a question. It was, after all, the the experts were clustered around the single chair. Korvin was "Sometimes," Korvin said. "It has other names?" the Ruler said. "It has no name," Korvin said truthfully. The Tr'en idiom was like the Earthly one "I do," Korvin said, "for convenience." "Not with exactitude," Korvin said. The key question had, at last, been asked. Korvin felt grateful that the logical Tr'en had determined to begin from the beginning, instead of going off after details of armament first "The answer to that question," Korvin said, "cannot be given to you." Korvin shrugged. "The explanation cannot be given to you." "I will not," Korvin said. It was the signal for another conference. With some satisfaction, Korvin noticed that the Tr'en were becoming slightly puzzled they were no longer moving and speaking with calm assurance. Korvin shook his head earnestly. "I am attempting," he said, "not to "I request that I be allowed to ask a question," Korvin said. from a knot of Tr'en, inclined his head in Korvin's direction, and obey. In this way uniformity is gained, and this uniformity aids in the speed of possible action and in the weight of action. All Tr'en Korvin shook his head. "If you insist," he said, "I'll try it. But you Korvin nodded. "Yes." Korvin shrugged. "Not knowingly," he said. The Ruler flashed a look at the technicians handling the lie-detector. Korvin turned to see their "We have no need of one," Korvin said calmly. Korvin wondered, as the technicians argued, how long they'd take Korvin found himself the object of more attention than he had hoped On the third day Korvin escaped. Korvin thanked his lucky stars that their genius had been restricted entire plan, within seconds. But, then, it was lack of that insight that had called for this particular plan. That, and the political structure of the Tr'en. The same lack of insight let the Tr'en subconscious work on his escape without any annoying distractions in the way of deep messages, but he could send them. He sent one now. Mission accomplished the Tr'en aren't about to come marauding out into space too soon. They've been given food for thought—nice indigestible food that's going to stick in

<question>:
Why did Korvin have to word his questions to the guard carefully?

<options>:
A Because he wanted the guard to give him something to do
B Because otherwise he would be harmed
C Because he did not know the Tr'en language
D Because the Tr'en do not infer the situational meaning of a question

<answer>:

D