电子邮件系统中，发送邮件协议为SMTP协议，使用的端口号是（ ）。
E-mail系统相关的有如下协议：
（1）SMTP：简单邮件传送协议，用于邮件的发送，工作在25号端口。
（2）POP3：邮局协议V3.0，用于接收邮件，工作在110号端口。
SNMP简单网络管理协议，默认传输层协议为UDP 25号端口。
HTTP超文本传输协议，默认传输层协议为TCP 80号端口。
ICMP is short for Internet（ ）Message Protocol, and is an integral part of the Internet（ ）suite (commonly referred to as TCP/IP). It is a（ ）layer protocol used by network devices to diagnose network communication issues. IP is not designed to be absolutely reliable. ICMP is to provide feedback about problems in the communication environment, not to make IP（ ）.One of the most well-known and useful messages in an ICMP datagram is the Destination（ ）message which is generated for several reasons, including unable to reach a network, a host, aport, or a protocol.
ICMP is short for Internet（ ）Message Protocol, and is an integral part of the Internet（ ）suite (commonly referred to as TCP/IP). It is a（ ）layer protocol used by network devices to diagnose network communication issues. IP is not designed to be absolutely reliable. ICMP is to provide feedback about problems in the communication environment, not to make IP（ ）.One of the most well-known and useful messages in an ICMP datagram is the Destination（ ）message which is generated for several reasons, including unable to reach a network, a host, aport, or a protocol.
ICMP is short for Internet（ ）Message Protocol, and is an integral part of the Internet（ ）suite (commonly referred to as TCP/IP). It is a（ ）layer protocol used by network devices to diagnose network communication issues. IP is not designed to be absolutely reliable. ICMP is to provide feedback about problems in the communication environment, not to make IP（ ）.One of the most well-known and useful messages in an ICMP datagram is the Destination（ ）message which is generated for several reasons, including unable to reach a network, a host, aport, or a protocol.
ICMP is short for Internet（ ）Message Protocol, and is an integral part of the Internet（ ）suite (commonly referred to as TCP/IP). It is a（ ）layer protocol used by network devices to diagnose network communication issues. IP is not designed to be absolutely reliable. ICMP is to provide feedback about problems in the communication environment, not to make IP（ ）.One of the most well-known and useful messages in an ICMP datagram is the Destination（ ）message which is generated for several reasons, including unable to reach a network, a host, aport, or a protocol.
ICMP is short for Internet（ ）Message Protocol, and is an integral part of the Internet（ ）suite (commonly referred to as TCP/IP). It is a（ ）layer protocol used by network devices to diagnose network communication issues. IP is not designed to be absolutely reliable. ICMP is to provide feedback about problems in the communication environment, not to make IP（ ）.One of the most well-known and useful messages in an ICMP datagram is the Destination（ ）message which is generated for several reasons, including unable to reach a network, a host, aport, or a protocol.
电子邮件系统中，发送邮件协议为SMTP协议，使用的端口号是（ ）。
可以通过电子邮件发送的文件类型有（ ）。
①视频文件②音频文件③图片文件④文本文件
下列关于ping命令的描述中，说法错误的是（ ）。
在Windows中，执行（ ）命令可以查看域名信息。
在Windows中，要查看到目标主机Alice的路径，可使用（ ）命令。
