* Generators are devices that convert mechanical energy into electrical energy. The process involves rotating a coil of wire within a magnetic field, which induces an alternating current (AC).

Let's look at the other options:

* (a) Battery: Batteries produce direct current (DC), which flows in one direction.

* (c) Chemical cells wired in series: Series wiring increases the voltage of a battery, but it still produces DC.

* (d) Chemical cells wired in parallel: Parallel wiring increases the current capacity of a battery, but it still produces DC.

In summary: Generators are the primary source of AC current.