In HTTP response message, if the requested HTTP protocol version is not supported, the status code is( ).
A. 200
B. 301
C. 400
D. 505
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The widely used port number of web application is( ).
A. 25
B. 20
C. 80
D. 53
HTTP has a mechanism that allows a cache to verify that its objects are up to date. The mechanism is( ).
A. persistent connections
B. cookies
C. Web Caching
D. conditional GET
In the following descriptions about persistent connection, which one is not correct?( )
A. The server leaves the TCP connection open after sending a response.
B. Each TCP connection is closed after the server sending one object.
C. There are two versions of persistent connection: without pipelining and with pipelining.
D. The default mode of HTTP uses persistent connection with pipelining.
FTP uses two parallel TCP connections to transfer a file, there are( ).
A. control connection and data connection
B. receiving connection and sending connection
C. client connection and sever connection
D. program connection and process connection
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