Here is your answer
D. [tex]<font color="red">the area where the magnetic force is exerted.</font>[/tex]
REASON :
A magnetic field is defined as the area where the influence of magnetic force can be experienced by placing a magnetic compass (deflection is shown in needle) or by bringing a charged particle near it.
The figure shows field lines around a bar magnet. At every point of field lines the magnetic force is experienced.
[tex]<marquee>[/tex]
HOPE IT IS USEFUL
