● A glue that holds the whole Internet together is the network layer protocol,(71). Unlike most older network layer protocols, it was designed from the beginning with internetworking in mind. Its job is to provide a -(72) way to transport datagrams from source to destination, without regard to whether these machines are on the same network or whether there are other networks in between them.
Communication in the Internet works as follows. The (73)layer takes data streams and breaks them up into datagrams. Each datagram is transmitted through the Internet, possibly being fragmented into smaller units as it goes. When all the pieces finally get to the destination machine, they are reassembled by the
(74) layer into the original datagram. This datagram is then handed to the transport layer, which inserts it into the receiving process' input stream.
An IP datagram consists of a header part and a text part. The header has a (75) part and a variable length optional part.
(71) A. IP (Internet Protocol)
B. IP (Interworking Protocol)
C. TCP (Transport Control Protocol)
D. TCP (Transfer Communication Protocol)
(72) A. best-quality
B. quality-guaranteed
C. connection-oriented
D. best-efforts
(73) A. data link
B. transport
C. network
D. application
(74) A. data link
B. transport
C. network
D. application
(75) A. 40-byte fixed
B. 64-byte fixed
C. 20~64 bytes variable
D. 20-byte fixed
第1题
抽样调查有很多优点,下列哪项不是其优点
A、节省人力
B、节省物力
C、工作细致
D、节省时间
E、适合于调查患病率低的疾病
第3题
抽样调查方法中,哪项不是它的优点
A.节省人力、物力
B.节约经费
C.调查范围小
D.调查工作容易做得细致
E.适用于调查变异较大的资料或发病率低的疾病
第4题
抽样调查方法中,哪项不是它的优点
A.节省人力、物力
B.节约经费
C.调查范围小
D.调查工作容易做得细致
E.适用于调查变异较大的资料或发病率低的疾病
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