BGP is an inter-autonomous system routing protocol; it is designed to be used between multiple autonomous ___40___. BGP assumes that routing within an autonomous system is done by an intra-autonomous system routing protocol. BGP does not make any assumptions about intra-autonomous system ___41___ protocols employed by the various autonomous systems. Specifically, BGP does not require all autonomous systems to run the same intra-autonomous system routing protocol.

BGP is a real inter-autonomous system routing protocol. It imposes no constraints on the underlying Internet topology. The information exchanged via BGP is sufficient to construct a graph of autonomous systems connectivity from which routing loops may be pruned and some routing. ___42___ decisions at the autonomous system level may be enforced.

The key feature of the protocol is the notion of Path Attributes. This feature provides BGP with flexibility and expandability. Path ___43___ are partitioned into well-known and optional. The provision for optional attributes allows experimentation that may involve a group of BGP ___44___without affecting the rest of the Internet. New optional attributes can be added to the protocol in much the same fashion as new options are added to the Telnet protocol, for instance.

40（）

A.routers 

B.systems 

C.computers 

D.sources

某旅行社10月份组织一个共100人的旅行团旅游，向每人收取旅游费5000元。旅游期间由旅行社为每人支付住宿费2000元，餐费1000元，交通费700元，门票300元。旅游业适用营业税税率为 5%，旅行社该项业务应缴纳营业税( )元。

A．20000

B．1000

C．25000

D．5000