选择题：The defacto standard Application Program Interface （API） for TCP/IP applications

The defacto standard Application Program Interface （API） for TCP/IP applications is the “sockets” interface. Although this API was developed for （　　） in the early 1980s it has also been implemented on a wide variety of non-Unix systems。 TCP/IP （　　）written using the sockets API have in the past enjoyed a high degree of portability and we would like the same （　　）with IPv6 applications。 But changes are required to the sockets API to support IPv6 and this memo describes these changes。These include a new socket address structure to carry IPv6 （　　），new address conversion functions，and some new socket options。These extensions are designed to provide access to the basic IPv6 features required by TCP and UDP applications，including multicasting， while introducing a minimum of change into the system and providing complete （　　）for existing IPv4 applications。
问题1选项
A.Windows
B.Linux
C.Unix
D.DOS
问题2选项
A.applications
B.networks
C.protocols
D.systems
问题3选项
A.portability
B.availability
C.capability
D.reliability
问题4选项
A.connections
B.protocols
C.networks
D.addresses
问题5选项
A.availability
B.compatibility
C.capability
D.reliability