The correct answer is: D. a sequence controller
A drum timer is a type of sequential controller that uses a rotating drum to control the sequence of events in a process. The drum is divided into a series of slots, each of which contains a set of instructions. The instructions are executed one at a time as the drum rotates.
A drum timer is a good example of a sequence controller because it controls the sequence of events in a process. The drum timer is not an output actuator, input sensor, or position sensor.
An output actuator is a device that converts electrical signals into mechanical motion. An input sensor is a device that converts physical quantities into electrical signals. A position sensor is a device that measures the position of an object.