(A) Moving with a constant velocity: This will produce an electric as well as a magnetic field, but not electromagnetic radiation.
(B) Moving in a circular orbit: This is the correct answer. An accelerating charge, such as one moving in a circular orbit, emits electromagnetic radiation.
(C) At rest: A stationary charge produces only a static electric field, not electromagnetic waves.
(D) Moving parallel to the magnetic field: This produces an electric and magnetic field, not EM radiation
The correct answer is (B): Moving in a circular orbit