Certain contacts of a mechanical timing relay are designed to operate at a preset time interval:

A) after the coil is energized.
B) after the coil is de-energized.
C) after power is applied to the circuit.
D) after the coil is energized or de-energized.

Mechanical timing relays can be designed to operate their contacts at a preset time interval either after the coil is energized or after it is de-energized, depending on the specific application and design of the relay. This allows for flexibility in controlling the timing of electrical circuits.