(C) A solenoid
The magnetic field of a current-carrying solenoid is similar to that of a bar magnet, with one end acting as north pole and the other as south pole.
Source: Section 12.2.4, Chapter 12
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The key fact from the textbook is: "The magnetic field of a solenoid carrying a current is similar to that of a bar magnet." A circular loop produces a field at its centre, but a solenoid (many turns wound cylindrically) replicates the complete dipole field pattern of a bar magnet — this is the distinguishing point examiners test. Do not confuse a solenoid with a single circular loop or coil.