Option D is correct because the magnetic field around a long straight current-carrying wire consists of concentric circles centered on the wire. This is established in the context which discusses the pattern of magnetic field lines produced around a current-carrying straight wire. The context further explains that these concentric circles representing the magnetic field become larger and larger as we move away from the wire, indicating the field strength decreases with distance. The other options are incorrect: the field lines are not straight lines (parallel or perpendicular to the wire), nor are they radial lines originating from the wire. The concentric circular pattern is a fundamental characteristic of the magnetic field produced by a straight current-carrying conductor.