单项选择题Wide Area Network (WAN) is a computer network that covers a broad areA. Which statement is correct for wide-area network (WAN)?()
A.Connects client devices wireless protocol
B.Crosses metropolitan, regional, or national boundaries
C.Limited in a single building, a group of buildings, or even a single room
D.Encompasses an entire city or metropolitan area and connects multiple local-area networks (LANs)