Question

electromagnet? a coil of wire b transistor array c fiber optic bundle d bank of capacitors

Explanation:

An electromagnet works by passing an electric current through a coil of wire, which creates a magnetic field. A transistor array is for signal processing, a fiber optic bundle is for light transmission, and a bank of capacitors stores electrical energy, none of which are part of an electromagnet's structure.

Answer:

A. coil of wire