By convention, a magnet has a north pole and a south pole. There is nothing called a positive pole and a negative pole in magnets. Hence, options C and D are false. In the case of a magnet, the magnetic lines emanate from the north pole and enter into the south pole. Hence option A is correct. One can trace the path of magnetic lines of a magnet. For this, place the magnet on a piece of white paper and place a magnetic compass right next to the north pole and trace the path of magnetic lines. As we move the magnetic compass, we will notice that a closed loop is formed between north and south poles of the magnet. The spacing between the magnetic lines gives us an idea of the strength of the magnetic field.
Hope this helps.