玻璃仪器常附着难清洗的物质，下列清洗方法不可行的是

A．内壁有碳酸钙的试管用稀盐酸清洗

B．内壁有碘的试管用酒精清洗

C．内壁有铁锈的试管用氢氧化钠溶液清洗

D．内壁有植物油的试管用洗洁精清洗

Networks can be interconnected by different devices. In the physical layer, networks can be connected by (41) or hubs, which just move the bits from one network to an identical network. One layer up we find bridges and switches, which operate at data link layer. They can accept (42) , examine the MAC address, and forward the frames to a different network while doing minor protocol translation in the process. In the network layer, we have routers that can connect two networks. If two networks have (43) network layer, the router may be able to translate between the packet formats. In the transport layer we find transport gateway, which can interface between two transport connections. Finally, in the application layer, application gateways translate message (44) . As an example, gateways between Internet E-mail and X.400 E-mail must (45) the E-mail message and change various header fields.

A．special

B．dependent

C．similar

D．dissimilar