Final answer:
Lodestones, suspended by a string, align with the Earth's magnetic field due to their naturally magnetized iron oxide content, pointing consistently in a north-south direction and acting like a natural compass.
Step-by-step explanation:
When lodestones are suspended by a piece of string, they will align themselves with the Earth's magnetic field. This phenomenon occurs because lodestones contain magnetite, which is a naturally magnetized form of iron oxide, and they possess magnetic properties similar to a compass. If left free to rotate, they will consistently point in a north-south direction. This natural orientation of lodestones was historically significant, as it led to the development of the early navigational compass. Magnetic field lines are defined to have the direction that a small compass points when placed at a location, which means that the compass needle aligns tangentially to the field lines.
Due to the Earth's magnetic field, the north pole of a magnet (or lodestone) will point towards the geographic North Pole, which is actually a magnetic south pole, and vice versa, hence answering option (D) - They align with the Earth's magnetic field.