複選題

30.Which of the following are accurate statements?
(A) The magnetic force on a wire carrying current is greatest when the wire is perpendicular to the magnetic field.
(B) A magnetic field line is tangent to the direction of the magnetic force on a moving charge.
(C) When a loop carrying current is put into a magnetic field, the loop plane tends to line up with the field.
(D) Magnetic field lines have north and south poles as their sources.
(E) The magnetic force on a moving charge does not change its energy.