题目内容：
BGP runs over a reliable transport （ ）. This eliminates the need to implement explicit update fragmentation, retransmission, acknowledgement, and （ ）. Any authentication scheme used by the transport protocol may be used in addition to BGP's own （ ）mechanisms. The error notification mechanism used in BGP （ ）that the transport protocol supports a “graceful” close, i.e., that all outstanding data will be delivered （请作答此空）the connection is closed.
A.after
B.before
C.earlier
D.concurrently
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答案解析：