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 he couldn't even alter the to the wonder and amazement of his Tr'en captors. He could do, as a matter of fact, precisely nothing. He wished quietly 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 all the advance reports, were likely to be pretty boring, but they'd have been better than nothing. 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 discuss almost anything from philosophy to plumbing, but there was nobody to discuss it with. He changed position on the bunk and stared at the walls. The Tr'en were efficient there weren't even any imperfections in the smooth surface to distract him. his captors had left him with a 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 be rigidly limited to humanoid types on oxygen planets really didn't care about it it was none of his business. The Tr'en regarded him narrowly through catlike pupils. "You are 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 his captors had no more resources than the ones he saw: a small translucent pistollike affair in a holster at the Tr'en's side, and a "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 across. It reminded him of some of the mathematical metalanguages he'd but it was, he admitted, better than solitude. "I am leaning against the door," Didyak said. The Tr'en literalist approach to the smallest problems of everyday living was a little hard "Why did you come to me?" he said at last. Didyak beamed at him. The sight was remarkably unpleasant, involving as it did the disclosure of the Tr'en fifty-eight teeth, mostly pointed. Korvin stared back impassively. "I have been ordered to come to you," Didyak said, "by the Ruler. The Ruler wishes to talk with It wasn't quite "talk" that was a general word in the Tr'en language, 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. of some metallic substance, and even the drapes were tan. It was, Korvin decided, much too much of a bad idea, even when the color 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 either side of their captive, looking as impassive as jade statues, six and a half feet high. "Within what limits?" 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 went on, "who are never more than a foot and a half in height, and usually less than that—approximately nine or ten inches. We call these children said apologetically. "Slipshod," the Ruler muttered. "A clumsy lie," the Ruler said. "The ship crashed wonder enough, but adapting the perilously delicate mechanisms that necessarily made up any lie-detector machinery was almost a miracle. 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 He hoped the lie-detector had been adjusted correctly. If it showed him telling an untruth, he wasn't likely to live long, and his job—not to mention the strongest personal inclinations—demanded most "I am not," he said. shall find out more about your job. Was the crash intentional?" , nor did it mean exactly that. As nearly as Korvin could make out, it meant "disposed of for all time." "No," he said. The Ruler roared. "Do not waste time with the obvious!" he shouted. logic"—the Tr'en word seemed to mean right-saying —"who will advise anybody on the planet. The barber who did, or didn't, shave himself, 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. The experts blinked. "Good?" he said. The expert frowned horribly, showing all of his teeth. Korvin did his best not to react. "Your plan is a failure," the expert said, "and you call this a good thing. You can mean only that your plan is different There was a short silence. The expert beamed. He examined the "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 the logical Tr'en had determined to begin from the beginning, instead of going off after details of armament first The Ruler turned to a group of his experts and a short muttered "Then you will suffer unpleasant consequences if you describe it to "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 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 won't understand it." wasn't making any sense. "I told you you wouldn't understand it," he "It is a defect in your explanation," the Ruler almost snarled. "You are lying," the expert said. One of the technicians chimed in: "The machine tells us—" "Then the machine is faulty," the expert said. "It will be corrected." Korvin wondered, as the technicians argued, how long they'd take studying the machine, before they realized it didn't have any defects he hadn't thought it would be. Even the most problem was insoluble. And the Tr'en weren't capable of that sort of thinking. 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 he couldn't receive 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 their craws until they finally manage to digest it. But they can't digest it and stay what they are you've got to be

<question>:
The text says "The expert frowned horribly." What makes the expert's smile so horrible?

<options>:
A The frown indicates that he's close to detecting Korvin's true motivations.
B The frown indicates that he knows that Korvin switched the wires on the lie detector.
C The frown is a signal to the Ruler that Korvin is lying.
D The frown is physically horrible because the Tr'en have fifty-eight, pointed teeth.

<answer>:

D