Cost，variable可变成本

可变成本（Variable cost）

连续型变量(continuous variable)

temp=’this is a temped variable’；echo foo${temp}上述命令执行的结果为（）

A:foo B:foo$temp C:foo’this is a temped variable’ D:foothis is a temped variable

variable的作用是（）。

A:指定环境变量名 B:指定要指派给变量的一系列字符串 C:显示出所有系统环境变量 D:错误命令

情境变量(situational variable)

(65) is the address of a variable or a variable in which the address of another variable is stored．

A:Director B:Record C:Array D:Pointer

______ is the address of a variable or a variable in which the address of another variable is stored.

A:Director B:Pointersystem C:Array D:Record

(75) is the address of a variable or a variable in which the address of another variable is stored.

A:Director B:Pointer C:Array D:Record

A glue that holds the whole Internet together is the network layer protocol, (1) .Unlike most older network layer protocols, it was designed from the beginning with internetworking in mind. Its job is to provide a (2) way to transport data grams 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 (3) layer takes data streams and breaks them up into data grams. 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 (4) 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 (5) part and a variable length optional part.

A:40-byte fixed B:64-byte fixed C:20～64 bytes variable D:20-byte fixed