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

<passage>:
lady before, except in the old magazines—Sis is just a kid and Ma is pretty sick and miserable—and it gave me such a start that I dropped the pail. Who wouldn't, knowing everyone on Earth was dead except Pa and Ma and Sis and you? Even at that, I don't suppose I should have been surprised. We all see things now and then. Ma has some pretty bad ones, to judge from the way she bugs her eyes at nothing and just screams and screams and huddles back against the blankets hanging around the Nest. Pa says it is natural we should react like that sometimes. When I'd recovered the pail and could look again at the opposite apartment, I got an idea of what Ma might be feeling at those times, for I saw it wasn't a young lady at all but simply a light—a tiny Against one of the blanket-walls is a big set of shelves, with tools and books and other stuff, and on top of it a whole row of clocks. Pa's and does a lot more besides. One of us must always watch it. Some of the clocks are alarm and we can use them to remind us. In the early days there was only Ma to take turns with Pa—I think of that when she gets difficult—but now there's me to help, and Sis too. It's Pa who is the chief guardian of the fire, though. I always think of him that way: a tall man sitting cross-legged, frowning anxiously at the fire, his lined face golden in its light, and every so often pail from me and bawl me out for loitering—he'd spotted my frozen helmet right off. That roused Ma and she joined in picking on me. She's always trying to get the load off her feelings, Pa explains. He shut 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 Nest, you could really feel its coldness. It just seemed to suck 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 low. Pa always keeps a big reserve supply of it in buckets behind the first blankets, along with extra coal and cans of food and other hand where she'd lost three fingers from frostbite inside the good one, as usual. I could tell that Pa was annoyed at me scaring her and wanted to explain it all away quickly, yet could see I wasn't fooling. Ma started moaning again, "I've always known there was something outside there, waiting to get us. I've felt it for years—something that's part of the cold and hates all warmth and wants to destroy the 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. "Sis," Pa said quietly, "come watch the fire. Keep an eye on the air, too. If it gets low or doesn't seem to be boiling fast enough, fetch another bucket from behind the blanket. But mind your hands. Use the cloth to pick up the bucket." Sis quit helping Ma be frightened and came over and did as she was told. Ma quieted down pretty suddenly, though her eyes were still kind of wild as she watched Pa fix on his helmet tight and pick up a pail and the two of us go out. Pa led the way and I took hold of his belt. It's a funny thing, I'm not afraid to go by myself, but when Pa's along I always want to hold on to 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 lurking out there, watching, waiting, getting ready. Inside, he said to me, touching helmets, "If you see something like that again, son, don't tell the others. Your Ma's sort of nervous these days and we owe her all the feeling of safety we can give her. Once—it was when your sister was born—I was ready to give up and die, but your 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 of you, too." "You know that game we sometimes play, sitting in a square in the Nest, the Nest and took off our outside clothes, Pa laughed about it all and told them it was nothing and kidded me for having such an imagination, 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 courage-ball. Something had to be done, and almost before I knew what I was going to say, I heard myself asking Pa to tell us about the old He sometimes doesn't mind telling that story, and Sis and I sure like to listen to it, and he got my idea. So we were all settled around the fire in a wink, and Ma pushed up some cans to thaw for supper, and Pa every bit of warmth just to keep alive. And how can they have hoped to end danger, any more than we can hope to end the cold? Sometimes I think Pa exaggerates and makes things out too black. He's little while—pulling it this way and that, like two dogs growling over a bone, Pa described it this time—and then the newcomer won and You see, Pa and some scientist friends of his had figured out part of airtight walls and doors, and insulation against the cold, and big supplies of food and fuel and water and bottled air. But the place got smashed in the last earthquakes and all Pa's friends were killed warmth and food. They're all still and stiff as statues, of course, but just like life. Pa showed them to me once in quick winks of his flashlight, when a little light. They scared me pretty bad and made my heart pound, especially the young lady. Now, with Pa telling his story for the umpteenth time to take our minds off another scare, I got to thinking of the frozen folk again. All of a skin tightened all over me. Pa was telling about the early years in the Nest and had come to the place where he philosophizes. let out a second whoop, waking Ma from her faint.) But if we were flabbergasted at them, they were double-flabbergasted at 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 all that. Ma had perked up wonderfully and was showing the young lady her cooking and sewing stuff, and even asking about how the women dressed at Los Alamos. The strangers marveled at everything and praised all and just asked bushels of questions. In fact, there was so much talking and excitement that Pa forgot about to Ma all the time and hid her face when anybody looked at her. I felt pretty uncomfortable and disturbed myself, even about the young lady. as if that were taken for granted, I could see that something of the same feeling struck Pa and Ma, too. Pa got very silent all of a sudden and Ma kept telling the young lady, "But I wouldn't know how to act there and I haven't any clothes." hankering to see them for myself. You ask me, Pa wants to see them, too. He's been getting pretty thoughtful, watching Ma and Sis perk up. "It's different, now that we know others are alive," he explains to me. "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." the way it was in the beginning." I guess he's right. You think the beautiful young lady will wait for me

<question>:
What is the relationship like between Ma and Pa?

<options>:
A They devotedly support each other
B They hardly speak anymore due to the hardships of survival
C They fight terribly at times
D Pa is like a caregiver for Ma given her affliction

<answer>:

D