BGP  is  an inter-autonomous  system routing  protocol;  it  is  designed  to  be  used between  multiple autonomous     (1)   . BGP assumes that routing within an autonomous system is done by an intra -autonomous  system  routing  protocols. BGP does not make any assumptions about any autonomous system  (2)  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 (3)   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 extensibility. Path (4) are partitioned into well-known and optional. The provision for optional attributes  allows experimentation that may  involve  a  group  of BGP (5)  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.
( 1)  A.  routers
B.  systems
C . computers
D.  source
( 2 )  A.  routing
B.  switching
C.  transmitting
D.  receiving
(3)  A . connection
B.  policy
C.  source
D.  consideration
(4 )   A.  states
B.  searches
C. meters
D.  costs
( 5 )  A.  routers
B.  states
C. meters
D. costs