A diagram for the magnetic field around a current-carrying straight conductor shows the following features:
1. Concentric circular field lines centred on the conductor.
2. Spacing between successive circles increases with distance from the conductor.
3. Two of the circles intersect each other at one point.
Which of these features are consistent with the known properties of magnetic field lines?
a) 1 and 3 only
b) 2 and 3 only
c) 1 and 2 only
d) 1, 2 and 3