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

<passage>:
Extensive research did not uncover any evidence that light that moved stealthily from window to window, just as if one investigate why the Earth had gone away from the Sun, and maybe to hunt down something to torment or terrify, now that the Earth didn't have into air, because there's no sound outside in the vacuum, of course. But my mind was still crawly and uneasy as I pushed through the last blankets—Pa's got them faced with aluminum foil to hold in the heat—and came into the Nest. four of us and our things. The floor is covered with thick woolly rugs. Three of the sides are blankets, and the blankets roofing it and without a sun or moon, that would be easy to do. tells me there used to be guardians of the fire sometimes in the very old days—vestal virgins, he calls them—although there was unfrozen It slowly melts and vanishes and refreshes the Nest and feeds the fire. The blankets keep it from escaping too fast. Pa'd like to seal the whole place, but he can't—building's too earthquake-twisted, and besides he has to leave the chimney open for smoke. Pa says air is tiny molecules that fly away like a flash if there isn't something to stop them. We have to watch sharp not to let the air run low. Pa always keeps a big reserve supply of it in buckets behind things, such as pails of snow to melt for water. We have to go way down to the bottom floor for that stuff, which is a mean trip, and get it through a door to outside. or the other, though it's the biggest part of the blanket. On top of that and easy to get at, which is lucky for us, there's the oxygen that keeps us alive. Pa says we live better than kings ever did, breathing pure oxygen, but we're used to it and don't notice. Finally, at the very top, there's a slick of liquid helium, which is funny stuff. All of these gases in neat separate layers. Like a pussy caffay, Pa the entry-slit in the blankets and wringing her hands together—the to explain it all away quickly, yet could see I wasn't fooling. comes crawling toward the Nest, just like an animal snuffing for lightning—not even Pa could figure where it came from—hit the nearby cans, but they keep heat and air in and can replace the air for a little while, long enough for our trips for water and coal and food and so on. Pa had everything on but his helmet. He knelt by the fireplace and on the roof to check if it's working all right. That's our worst trip and Pa won't let me make it alone. him. Habit, I guess, and then there's no denying that this time I was a bit scared. You see, it's this way. We know that everything is dead out there. Pa heard the last radio voices fade away years ago, and had seen some of the last folks die who weren't as lucky or well-protected as us. So we knew that if there was something groping around out there, it couldn't be anything human or friendly. Besides that, there's a feeling that comes with it always being night, cold I found myself wondering whether there mightn't be something on the first and known it wasn't so. around inside them now, or anywhere else. To my surprise, Pa didn't it only so long, and then he's got to toss it to someone else. When it's tossed your way, you've got to catch it and hold it tight—and hope there'll be someone else to toss it to when you get tired of being brave." but his words fell flat. He didn't convince Ma and Sis any more than he did me. It looked for a minute like we were all fumbling the I was going to say, I heard myself asking Pa to tell us about the old It was the same old story as always—I think I could recite the main Wanting it even, or at least wishing it were over so as to end their nervousness. As if all folks didn't have to hang together and pool every bit of warmth just to keep alive. And how can they have hoped to to keep it a secret from most people, but then the truth came out, on the other side. But then they found it wasn't going to hit either side, but was going to come very close to the Earth. You see, the dark star was going through space faster than the Sun, and in the opposite direction, and it had to wrench the world considerably in order to take it away. buildings toppled, oceans slopped over, swamps and sandy deserts gave great sliding surges that buried nearby lands. Earth was almost jerked You see, Pa and some scientist friends of his had figured out part of would freeze—and they'd been working like mad to fix up a place with airtight walls and doors, and insulation against the cold, and big supplies of food and fuel and water and bottled air. But the place lay his hands on. I guess he's telling pretty much the truth when he says he didn't have because the dark star was pulling us away very fast and because Earth's warmth and food. They're all still and stiff as statues, of course, but just like life. molecules ought to freeze solid forever? Or like the electricity that dark star to get us. eyes, creeping, crawling, snuffing their way, following the heat to the There was just the sound of Pa's voice and the clocks. And then, from beyond the blankets, I thought I heard a tiny noise. My Pa was telling about the early years in the Nest and had come to the I got the answer." And still the steps kept shuffling closer. It seemed to me that the homemade ones, only fancier, and that the men were, too—and that the The silence kept on while I swallowed hard a couple of times, and after that there was all sorts of jabbering and commotion. They were simply people, you see. We hadn't been the only ones to we'd just thought so, for natural enough reasons. These three found out how They were from Los Alamos and they were getting their heat and power from atomic energy. Just using the uranium and plutonium intended for bombs, they had enough to go on for thousands of years. They had a regular little airtight city, with air-locks and all. They even generated electric light and grew plants and animals by it. (At this Pa let out a second whoop, waking Ma from her faint.) us. One of the men kept saying, "But it's impossible, I tell you. You can't maintain an air supply without hermetic sealing. It's simply impossible." That was after he had got his helmet off and was using our air. Meanwhile, the young lady kept looking around at us as if we were They'd been scouting around for survivors, but they never expected to find any in a place like this. They had rocket ships at Los Alamos and plenty of chemical fuel. As for liquid oxygen, all you had to do was go out and shovel the air blanket at the top level decided to make some trips to likely places where there might be other survivors. No good trying long-distance radio signals, of course, since there was no atmosphere to carry them around the curve of the Earth. Well, they'd found other colonies at Argonne and Brookhaven and way around the world at Harwell and Tanna Tuva. And now they'd been giving instrument that noticed the faintest heat waves and it had told them there was something warm down here, so they'd landed to investigate. Of course we hadn't heard them land, since there was no air to carry the sound, and they'd had to investigate around quite a while before finding us. Their instruments had given them a wrong steer and they'd that they found the Nest a bit smelly, but they never mentioned that at drunk. They weren't used to so much oxygen. boiling away and Ma and Sis sleeping in the warmth and the flickering just as if it was one of our birthdays or Christmas.

<question>:
Why couldn’t the search party find the family with traditional communications?

<options>:
A Signals are disrupted by the electromagnetic events of the dark star
B The family couldn’t hear them because they were underground
C The communication devices don’t work in the cold
D There is no medium to carry signals

<answer>:

D