Concept:A freely suspended compass needle aligns itself with the Earth's magnetic field lines.Explanation:The Earth has magnetic north and south poles.The vertical plane passing through these magnetic poles is called the magnetic meridian.A compass needle is a small magnet that is free to rotate horizontally.It always points along the horizontal component of the Earth's magnetic field.Therefore, the needle settles in the plane of the magnetic meridian, not the geographic meridian.Answer:B. magnetic meridian