The correct answer is D. Switchgear is a device used for switching, controlling, and protecting electrical circuits and equipment. It is used to isolate electrical equipment from the power supply for maintenance or repair, and to protect equipment from overcurrent, overvoltage, and other faults.
Option A is incorrect because switchgear does not only interrupt electrical circuits. It also switches and controls them.
Option B is incorrect because switchgear does not only switch electrical circuits. It also interrupts and controls them.
Option C is incorrect because switchgear does not only switch and control electrical circuits. It also protects them from overcurrent, overvoltage, and other faults.