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

<passage>:
had no stomach for mysteries, vast or trifling, and there number. Across to the right was a group that Baron knew the first passage to the core of Vulcan Crater on Venus. Baron I figured that it would pass off after a while. I was apprehensive no key to his age—he might have been thirty or a thousand—but “At perihelion?” and, for once, he didn’t have anything to say. It was the wreck where have you been hiding? their to. You’re the only man on Earth who’s an area of recent surface activity the surface was really treacherous. “You want to know why we failed?” asked Claney. “Of course we want to know. We “It’s simple. We failed because it can’t be done. We couldn’t much about the others. I was worried about It was the planet that whipped us, that and the Sun broad flat plateau, dodging a network of gaping surface cracks—winding solid rock. I couldn’t see far ahead, because of the yellow haze I think. I followed the news stories like a tri-V serial and then I know now that they were a pair of idiots, starting off without proper equipment, with practically no knowledge of surface conditions, without any charts—they couldn’t have made the Colony there. I first met him on Venus been out to see Sanderson and the Twilight Lab on Mercury, and how he preferred a hot trek to a cold one any day of the year—and then he wanted to know what I’d been doing since Venus and what my plans were. “That much!” he said. “Well, there can’t be much fat on you, at any rate. How do you take heat?” “You should know,” I said. “Venus was no icebox.” “No, I mean real dangerous, too.” “What trip?” “Brightside of Mercury,” the Major said. I whistled cautiously. “At aphelion?” He threw his head back. “Why try a Crossing at aphelion? about it.” He leaned across me eagerly. “I want to make a Crossing at perihelion and I want to cross on the surface. If a man can do that, he’s got Mercury. Until then, nobody’s got Mercury. I want Mercury—but I’ll need help getting it.” I’d thought of it a thousand times and never dared consider it. Nobody had, since Wyatt and Carpenter disappeared. Mercury turns on its axis in the same time that it wheels around the Sun, which means that the Brightside is always facing in. That makes the Brightside of Mercury at perihelion the hottest place in the Solar System, with one single exception: the surface of the Sun itself. It would be a hellish trek. Only a few men had ever learned hellish and they never came back to tell about it. It would cross it. I wanted to be along. The Twilight Lab, near the northern pole of Mercury, was the obvious jumping-off place. The setup there wasn’t very extensive—a crew sunk deep into the crust, and the tower that housed Twilight Lab wasn’t particularly interested in the Brightside, of course—the Sun was Sanderson’s baby and he’d picked Mercury as the closest chunk of rock to the Sun that could hold his observatory. He’d chosen a good location, too. On Mercury, the Brightside temperature hits 770° F. at perihelion and the Darkside runs pretty constant at -410° F. No permanent installation with a human crew could survive at either extreme. But with Mercury’s wobble, the twilight zone between for about seventy out of the eighty-eight days it takes the planet to wheel around. The Major was counting on Sanderson knowing something about Mercury as well as the Sun when we camped at the Lab to make final preparations. Sanderson did. He thought we’d lost our minds and he said this trek. I had a funny feeling that Jack really didn’t care for exploring too much, but he thought Mikuta was God, followed ever give you an answer that makes sense. Anyway, Stone had “Who’s he?” Stone wanted to know. I’d heard plenty of stories about Ted McIvers and I wasn’t say much about it. Stone was getting edgy and so was I. We they were. The best available were pretty poor, taken from so showed the biggest ranges of peaks and craters and faults, and down toward the equator—not only volcanic, but sub-surface The Major shrugged. “Well, it’s treacherous, there’s no It seemed that the more we considered the problem, the surface activity there was pretty much slowed down and localized. well. There was an atmosphere and a constant atmospheric had reached escape velocity and disappeared from Brightside millennia ago—but there was CO 2 , and nitrogen, and traces of other heavier gases. There was also an abundance of sulfur vapor, as well as carbon disulfide and sulfur dioxide. The atmospheric tide moved toward the Darkside, where it condensed, carrying enough volcanic ash with it for Sanderson to estimate the depth and nature of the surface upheavals on rocket from Venus. He’d missed the ship that the Major and I had taken by a few hours, and had conned his way to Venus Evidently the Major decided not to press the issue of his like this, and some of the best wouldn’t seem to be the most reliable at first glance. Anyway, personality problems weren’t one had an inner lining of a fiberglass modification, to avoid “They were insulated, too, but we weren’t counting on “You weren’t!” Baron exclaimed. “Why not?” with thirty days to make it to the Center of Brightside. If we could cross an average of seventy miles a day, we could hit Center exactly at perihelion, the point of Mercury’s closest approach to the Sun—which made Center the hottest part of the planet at the hottest it ever gets. The Sun was already huge and yellow over the horizon when we started, twice the size it appears on Earth. Every day that Sun would grow bigger and whiter, and every day the what terrain we had to cross. Detours would be dangerous and He stared at the Major. “I mean, how can we tell what sort of I can stay on good solid ground, of course, but scan the “But why not? We could save ourselves days!” It was hot. If I forget everything else about that trek, I’ll Even at only 30 per cent Earth gravity they were a strain on I kept my eyes pasted to the big polaroid binocs, picking out the track the early research teams had made out into the edge were in virgin territory and already the Sun was beginning to that glaring Sun and the baked yellow rocks going past, and reasons—but all we knew, or cared about, was that it We didn’t sleep the first few stops, as a consequence. Our the wheel. We were moving down into desolation that made with a barely visible yellowish mist of sulfur and sulfurous gases. It was a hot, barren hole, no place for any man to go, but the challenge was so powerful you could almost feel it. No one had ever crossed this land before and escaped. Those who had the hardest way possible: overland, through anything the land Yet we knew that even the land might have been conquered before, except for that Sun. We’d fought absolute cold before worse heat in the Solar System was the surface of the Sun itself. Brightside was worth trying for. We would get it or it would get us. That was the bargain. I learned a lot about Mercury those first few driving periods. The gorge petered out after a hundred miles and we moved onto the slope of a range of ragged craters that ran south and east. This range had shown no activity since the first landing on Mercury forty years before, but beyond it there were active cones. Yellow fumes rose from the craters constantly their sides were shrouded with heavy ash. face of the planet. Not enough for erosion, though. The craters rubble. Below were the vast yellow flatlands, smoking and hissing from the gases beneath the crust. Over everything was gray dust—silicates and salts, pumice and limestone and granite I learned to read the ground, to tell a covered fault by the

<question>:
Which planet wasn't well-known according to the text?

<options>:
A Jupiter
B Venus
C Mars
D Mercury

<answer>:

D