已知物质X符合下列转化关系：HCl + XMgCl₂ + H₂↑，则X可能是  [ ]

A.镁

B.氧化镁

C.锌

D.氢气

Traditional IP packet forwarding analyzes the （1）IP address contained in the network layer header of each packet as the packet travels from its source to its final destination. A router analyzes the destination IP address independently at each hop in the network. Dynamic （2） protocols or static configuration builds the database needed to analyze the destination IP address (the routing table). The process of implementing traditional IP routing also is called hop-by-hop destination-based（3） routing. Although successful, and obviously widely deployed, certain restrictions, which have been realized for some time, exist for this method of packet forwarding that diminish its （4）. New techniques are therefore required to address and expand the functionality of an IP-based network infrastructure. This first chapter concentrate on identifying these restrictions and presents a new architecture, known as multipleprotocol （5）switching, that provides solutions to some of these restrictions.

（4）是（）

A.reliability

B.flexibility

C.stability

D.capability