jolie builds a model of a maglev train. she uses disc magnets to levitate the train. a disc magnet has its north and south poles on its faces, as shown. what is the best way to arrange the magnets on the train and on the track so that the model train levitates? rot, so that the north pole of each magnet on the train points up and the north pole of each magnet on the track points up rot, so that the north pole of the magnets on the train points up and the north poles of the magnets on the track point down on edge, so that the north poles of the magnets on the train point to the front and the north poles of the magnet on the track point toward the rear on edge, so that the north pole of each magnet on the train and on the track point toward the rear of the train

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# Brief Explanations:
To levitate the train, magnetic repulsion is needed (like poles repel). For the train's magnets (north up) and track's magnets, if track's north is down (so train's north faces track's south? No, wait—wait, the disc magnet has N on top, S on bottom. Wait, no: the diagram shows N on the top face, S on the bottom face. So to repel, the train's magnet (top N) should face the track's magnet with top S (so track's magnet has N down, S up? Wait, no—magnetic poles: like poles repel. So if the train's magnet has N pole facing the track, the track's magnet should have N pole facing the train (repulsion) or S? Wait, no: north repels north, south repels south. So to levitate, the train's magnet and track's magnet must have like poles facing each other. Wait, the train is above the track. So the bottom of the train's magnet (wait, no—the train's magnet: the diagram shows N on top, S on bottom (the face towards the track). Wait, the disc magnet: the top face is N, bottom face is S. So the train has magnets with bottom face S? No, wait the diagram: the magnet is a disc, with N on the top (upper face) and S on the bottom (lower face, towards the track). So to levitate, the track's magnet must have a top face that repels the train's magnet's bottom face. The train's bottom face is S (since top is N, bottom is S). Wait, no—magnetic poles: a magnet has two poles, N and S. So if the train's magnet has N on top, then the bottom is S. So the track's magnet, to repel the train's S pole, would need to have S on top (since S repels S). But the options are about N poles. Wait, maybe I got the poles reversed. Wait, the question is about arranging the magnets so the train levitates. Levitation via magnetic repulsion: like poles (N-N or S-S) facing each other. So the train's magnet (on the train) has N pole pointing up (so bottom pole is S), or N pole pointing down (towards the track). Wait, the options:

Option 1: Train's N up, track's N up. So train's bottom pole (if N is up, bottom is S) vs track's top pole (N up, so bottom is S). No, that's S and N—attraction. Wait, no—maybe the magnet is oriented with N on the face towards the track. Wait, the diagram shows the disc magnet with N on the top (upper face) and S on the bottom (lower face, the face that would be towards the track if the magnet is on the train). So the train's magnet has lower face S. To repel, the track's magnet must have lower face S (so upper face N) or upper face S? No, like poles repel. So if the train's magnet has lower face S (towards track), the track's magnet must have upper face S (towards train) to repel (S-S). But the options are about N poles. Wait, maybe the magnet is oriented with N on the face towards the track. Let's re-express:

If the train's magnet has N pole pointing down (towards the track), then the track's magnet must have N pole pointing up (towards the train) to repel (N-N). Alternatively, if the train's N is up (so down is S), track's S is up (repel S-S). But the options:

Option 2: Train's N up (so down is S), track's N down (so up is S). Wait, no—option 2 says: "flat, so that the north pole of the magnets on the train point up and the north poles of the magnets on the track point down". So train's magnet: N up (so the face towards the track is S, because N and S are opposite). Track's magnet: N down (so the face towards the train is S, because N is down, so top face is S). So train's S (towards track) and track's S (towards train) – repulsion! That works. Wait, but the option says "north pole of the magnets on the train point up" (so train's magnet has N up, so bottom is S) and "north pole of the magnets on the track point down" (so track's magnet has N down, so top is S). So the two faces (train's bottom S and track's top S) are like poles, repelling each other, causing levitation. The other options:

Option 1: Train's N up, track's N up. So train's bottom S, track's top N – attraction (S and N attract), so train would be pulled down, not levitate.

Option 3: On edge, N towards front – that's for propulsion, not levitation (levitation is vertical, propulsion is horizontal).

Option 4: On edge, N towards front – same as 3, horizontal arrangement, not vertical levitation.

So the correct option is the second one: flat, train's N up, track's N down. Because that makes the train's bottom pole S (since N is up) and track's top pole S (since N is down, so top is S), so S-S repulsion, levitating the train.
# Answer:
B. flat, so that the north pole of the magnets on the train point up and the north poles of the magnets on the track point down

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