The e.m.f. (electromotive force) produced in a coil of wire when a magnet is moved through it is determined by Faraday's law of electromagnetic induction.

According to Faraday's law, the e.m.f. induced in a coil is directly proportional to the rate of change of magnetic flux through the coil.

The e.m.f. produced in the wire depends on all of the following factors:

1. The number of turns in the coil: More turns in the coil will result in a higher induced e.m.f.
2. The strength of the magnet: A stronger magnet will induce a higher e.m.f. in the coil.
3. The speed at which the magnet is moved: A faster movement of the magnet will result in a higher rate of change of magnetic flux and hence a higher induced e.m.f.

Therefore, the correct answer is D. All of the above.