Which of the following provides the best example of a solenoid?

a.
A long straight wire with one end connected to the positive terminal of a battery.

c.
A coil of wire looped around a permanent magnet.

b.
A coil of wire wrapped around a nail, with each end of the wire connected to the positive and negative terminals of a battery.

d.
A long loop of wire with each end connected to the positive and negative terminals of a battery.