如图4-3所示的树形文件系统中，方框表示目录，圆圈表示文件，“/”表示路径中的分隔符，“/”在路径之首时表示根目录。

假设当前目录是D1，进程A可以按以下两种方式打开同一个文件f1。  方式①  fd1=open(“/D1/W1/f1”,O_RDONLY)；  方式②  fd1=open(“(22)/f1”,O_RDONLY)；

(65)

(64)

(63)

(62)

以下IPv4地址中，属于单播地址的是(70)。

WAP uses (71) , which includes the Handheld Device Markup Language (HDML) developed by Phone.com. WML can also trace its roots to eXtensible Markup Language (XML). A markup language is a way of adding information to your (72) that tells the device receiving the content what to do with it. The best known markup language is Hypertext Markup Language. (73) HTML, WML is considered a meta. language. Basically, this means that in addition to providing predefined (74) , WML lets you design your own markup language (75) . WAP also allows the use of standard Internet protocols such as UDP, IP and XML.

根据整体设计的原则，网络系统安全必须包括安全防护机制、安全检测机制和(69)。

包过滤防火墙通过(68)来确定数据包是否能通过。

通常，客户端软件使用(67)协议将邮件传递到发送方的邮件服务器中。

接入Internet的方式有多种，下面关于各种接入方式的描述中，正确的是()。