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

<passage>:
You will, you know, so why quibble about it? At least, you always have ... or do ... or will. I don't know, verbs get all mixed up. We don't have the right attitude toward tenses for a situation like this. to it, of course, but it will take about thirty years. You're wondering whether to give me a drink, as I remember it. Why not? for the first time. Some kind of telepathy seems to work between two of the same people. You sense things. So I'll simply go ahead talking for half an hour or so, until you get over it. After that you'll come along with me. You know, I could try to change things around by telling what happened to me So let's begin when you get up in half an hour and come out with me. You'll take a closer look at the machine, then. Yes, it'll be pretty obvious it must be a time machine. You'll sense that, too. You've seen I'll be tired of talking by then, and in a hurry to get going. So I cut off your questions, and get you inside. I snap on a green button, and everything seems to cut off around us. You can see a sort of prevents passage through time from affecting us. The luggage section isn't protected, though. You start to say something, but by then I'm pressing a black button, there . You are completely outside of time and space, as best you can guess how things are. You can't feel any motion, of course. You try to reach a hand out arm back, you're still sound and uninjured. But it looks frightening and you don't try it again. Then it comes to you slowly that you're actually traveling in time. You turn to me, getting used to the idea. "So this is the fourth dimension?" you ask. traveling along it, you'd need a fifth. Don't ask me. I didn't invent the machine and I don't understand it." "But...." I let it go, and so do you. If you don't, it's a good way of going crazy. You'll see later why I couldn't have invented the machine. Of course, there may have been a start for all this once. There may have been a time when you did invent the machine—the atomic motor first, then the time-machine. And when you closed the loop by going back and saving yourself the trouble, it got all tangled up. I figured out once that such a universe would need some seven or eight time and space dimensions. It's simpler just to figure that this is the way time got bent back on itself. Maybe there is no machine, and it's just easier for us to imagine it. When you spend thirty years thinking about it, as Anyhow, you sit there, watching nothing all around you, and no time, apparently, though there is a time effect back in the luggage space. You look at your watch and it's still running. That means you either carry a small time field with you, or you are catching a small increment of time from the main field. I don't know, and you won't think about that then, either. time nor space, apparently. How could the air leak out? You still feel gravity, but I can't explain that, either. Maybe the machine has a gravity field built in, or maybe the time that makes your watch run is responsible for gravity. In spite of Einstein, you have always had the idea that time is an effect of gravity, and I sort of agree, still. Then the machine stops—at least, the field around us cuts off. You machine, just as I do. I've got a bundle of clothes and I start changing. It's a sort this century, as near as I can remember it, and I should be able to pass fairly well. I've had all my fortune—the one you make on that atomic generator—invested in such a way I can get it on using some back with you." You nod, remembering I've told you about it. "What century is this, anyway?" I'd told you that, too, but you've forgotten. "As near as I can guess, interstellar civilization." You take another cigaret from me, and follow me. I've got a small flashlight and we grope through a pile of rubbish, out into a corridor. "What about the time machine?" you ask. You go up the steps, but you see that it seems to be closed. You hesitate for a moment, then. You're beginning to think the whole affair is complete nonsense, and you should get back to the time machine and "Help you, sir? Oh, of course. You must be playing in 'Atoms and Axioms.' The museum's closed, but I'll be glad to let you study whatever you need for realism in your role. Nice show. I saw it twice." "Thanks," you mutter, wondering what kind of civilization can produce them to check his latest theory of how they work. Too bad he could his name. Either they don't know it, or they take it for granted that fact that they have the original model of the first atomic generator and full patent application. They state that it has all major refinements, operating on any fuel, producing electricity at any desired voltage up to five million, any chosen cyclic rate from direct current to one thousand megacycles, the cathogrids and we had to replace that, but otherwise it's exactly as the great inventor made it. And it still operates as well as ever. Like to have me tell you about it?" "Not particularly," you begin, and then realize bad manners might be moves. There's a little sign under it, indicating you shouldn't touch it, since the gravostatic plate is being renewed. Well, you won't be able to change the time cycle by doing anything I haven't told you, but a working model such as that is a handy thing. a machine geared for voice operation can make anything of that. What the original level. You get out—and realize you don't have a light. You'll never know what you stumbled over, but, somehow, you move back in the direction of the time machine, bumping against boxes, staggering here and there, and trying to find the right place by sheer feel. Then it's the weak light in the time machine. years"—and you begin waiting for the air to get stale. It doesn't because there is only one of you this time. Instead, everything flashes off and you're sitting in the machine in your own back yard. You'll figure out the cycle in more details later. You get into the machine in front of your house, go to the future in the sub-basement, land in your back yard, and then hop back thirty years to pick up yourself, landing in front of your house. Just that. But right then, It isn't hard to disassemble, but you don't learn a thing just some missing! It won't work. You put some #12 house wire in, exactly like the set on the other side, drop in some iron filings, and try it again. And with the controls set at 120 volts, 60 cycles and 15 amperes, you get just that. You don't need the power company any more. And you feel a little happier when you realize that the luggage space wasn't insulated from time effects by a field, so the motor has moved backward in time, somehow, and is back to its original youth—minus the replaced wires the guard mentioned—which probably wore out because of the makeshift job you've just done. It will begin to soak in, then. You pick up an atomic generator in the future and bring it back to the past—your present—so that it can be put in the museum with you as the inventor so you can steal it to be the inventor. And you do it in a time machine which you bring back to yourself to take yourself into the future to return to take back to yourself.... Who invented what? And who built which? One day you come across an old poem—something about some folks calling it evolution and others calling it God. You go out, make a few provisions for the future, and come back to climb into the time machine that's waiting in the building you had put around it. Then you'll be knocking on your own door, thirty years back—or right now, from your came looking for you and shouting, before the time machine left.

<question>:
What don't they know about the time machine?

<options>:
A who invented it
B what the third set of buttons do
C where it gets stored when not in use
D how to make it go back and forth in time

<answer>:

A