Switchboards may be of the dead-front type in which all live parts are installed behind （） and only the operation handles and instruments are on the front.

A.distribution boards
B.section boards
C.emergency switch boards
D.main switch boards

A.distribution boards
B.section boards
C.emergency switch boards
D.main switch boards

A.ultra much space
B.universal medium system
C.unit machined space
D.unattended machinery space