TCP functions at the Open System Interconnection (OSI) (61) layer, or Layer 4. Its chief responsibility is to ensure (62) end-to-end connectivity. IP, located one layer down, at the OSI network layer, or Layer 3, communicates the addresses of each (63) sender and receiver to the routers along the way. Routers and Layer 3 switches can read IP and other Layer 3 (64) . This information, combined with routing tables and other network intelligence, is all it takes to get (65) the room or around the world via TCP/IP.

A．better

B．protocols

C．protocol

D．good

关于委托合同，下列表述中正确的是( )。

A．委托合同为诺成合同和要式合同

B．委托合同可以是有偿的，亦可以是无偿的

C．受托人必须以委托人的名义为委托人处理事务

D．委托合同是当事人之间基于信任而订立

E．委托合同既可以采用口头形式，也可以采用书面形式