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

<passage>:
A Pail of Air By FRITZ LEIBER Illustrated by ED ALEXANDER eternal night and turning history into incredible myth in a single generation! Pa had sent me out to get an extra pail of air. I'd just about scooped it full and most of the warmth had leaked from my fingers when I saw the thing. fifth floor of the opposite apartment, which hereabouts is the floor just above the white blanket of frozen air. I'd never seen a live young the pail. Who wouldn't, knowing everyone on Earth was dead except Pa and Ma and Sis and you? air from the Nest, and I wasn't quite so scared. I began to hear the tick-ticking of the clocks in the Nest and knew I was getting back 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 Let me tell you about the Nest. It's low and snug, just room for the which there is a fire that must never go out. It keeps us from freezing air all around then and you didn't really need one. He was sitting just that way now, though he got up quick to take the her up pretty fast. Sis let off a couple of silly squeals too. Pa handled the pail of air in a twist of cloth. Now that it was inside the heat out of everything. Even the flames cringed away from it as Pa put it down close by the fire. Yet it's that glimmery white stuff in the pail that keeps us alive. 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 through a door to outside. You see, when the Earth got cold, all the water in the air froze first and made a blanket ten feet thick or so everywhere, and then down on top of that dropped the crystals of frozen air, making another white blanket sixty or seventy feet thick maybe. Of course, all the parts of the air didn't freeze and snow down at the same time. First to drop out was the carbon dioxide—when you're shoveling for water, you have to make sure you don't go too high and get any of that stuff mixed in, for it would put you to sleep, maybe for good, and make the fire go out. Next there's the nitrogen, which doesn't count one way 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 laughingly says, whatever that is. heat—that's the liquid helium. And once, when I was little, a bolt of lightning—not even Pa could figure where it came from—hit the nearby steeple and crawled up and down it for weeks, until the glow finally died. "Not like anything I ever saw," I told him. He stood for a moment frowning. Then, "I'll go out with you, and you on the roof to check if it's working all right. That's our worst trip afraid to go by myself, but when Pa's along I always want to hold on to be anything human or friendly. Besides that, there's a feeling that comes with it always being night, cold Earth. Just then we came to the end of the corridor and I followed Pa out on the balcony. I don't know what the city looked like in the old days, but now it's Mother kept me trying. Another time she kept the fire going a whole week all by herself when I was sick. Nursed me and took care of the two steady and warm, and the people on it fixing to make money and wars and have a good time and get power and treat each other right or wrong, Wanting it even, or at least wishing it were over so as to end their every bit of warmth just to keep alive. And how can they have hoped to unfrozen water!—and people seeing stars blotted out by something on a clear in order to take it away. out of its atmosphere blanket and the air got so thin in spots that people keeled over and fainted—though of course, at the same time, they were getting knocked down by the Big Jerk and maybe their bones airtight walls and doors, and insulation against the cold, and big supplies of food and fuel and water and bottled air. But the place others clustered around the furnaces in the basements where we go for a leg in splints. In another, a man and woman are huddled together in warmth and food. They're all still and stiff as statues, of course, but just like life. he still had a fair supply of batteries and could afford to waste forgotten about that on account of trying to hide it from the others. What, I asked myself, if the frozen folk were coming to life? What if they were like the liquid helium that got a new lease on life and started crawling toward the heat just when you thought its molecules ought to freeze solid forever? Or like the electricity that Nest. existence of hard work and cold and loneliness? The human race is done. "Life's always been a business of working hard and fighting the cold," we had all eternity ahead of us. I'd have children and teach them all enlarge and seal the Nest. I'd do what I could to keep everything survive 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 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 survivors. No good trying long-distance radio signals, of course, since there was no atmosphere to carry them around the curve of the Earth. 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 By now, all five adults were talking like sixty. Pa was demonstrating to the men how he worked the fire and got rid of the ice in the chimney and found the air had all boiled away in the pail. He got another bucket of air quick from behind the blankets. Of course that started them all laughing and jabbering again. The newcomers even got a little drunk. They weren't used to so much oxygen. Funny thing, though—I didn't do much talking at all and Sis hung on decided yet just what will happen. Maybe the Nest will be kept up as "Your mother doesn't feel so hopeless any more. Neither do I, for that matter, not having to carry the whole responsibility for keeping the human race going, so to speak. It scares a person." I looked around at the blanket walls and the fire and the pails of air boiling away and Ma and Sis sleeping in the warmth and the flickering light.

<question>:
What are the ways that the family sustains themselves?

<options>:
A Drinking water from under the ice of a frozen lake
B Eating the people that froze in the city
C Sheltering next to a nuclear reactor
D Breathing pure oxygen

<answer>:

D