8259A是为控制优先级中断而设计的可编程芯片，用于协助CPU管理中断源，下面关于其功能描述不正确的是______。

A．它具有中断源优先级排队、辨识中断源功能

B．向CPU提供中断向量等功能

C．中断请求信号INTA向CPU或者级联的上级8259A发出中断信号

D．每片8259A具有8根中断请求线IRQ0～IRQ7，作为外部中断请求输入信号

For each blank, choose the best answer from the four choices and write down on the answer sheet.
(21) is a six bytes OSI layer 2 address which is burned into every networking
device that provides its unique identity for point to point communication.
(22) is a professional organization of individuals in multiple professions which focuses on effort on lower-layer protocols.
(23) functions with two layers of protocols. It can connect networks of different speeds and can be adapted to an environment as it expands.
(24) is the popular LAN developed under the direction of the IEEE802.5.
(25) is the popular backbone technology for transmitting information at high speed with a high level of fault tolerance which is developed under the direction of ANSI.

A．The MAC address

B．The IP address

C．The subnet address

D．The virtual address