At which layer of the OSI model dose PPP perform？（）

物理层定义了『____』资源块和物理资源块。(Physical layer defines『____』resource block and the physical resource block .)

TCP/IP(71)layer protocols provide services to the application(72)running on a computer. The application layer does not define the application itself, but rather it defines(73)that applications need--like the ability to transfer a file in the case of HTTP. In short, the application layer provides an(74)between software running on a computer and the network itself. The TCP/IP application layer includes a relatively large number of protocols, with HTTP being only one of those. The TCP/IP(75)layer consists of two main protocol options--the Transmission Control Protocol(TCP) and the User Datagram Protocol(UDP).

A．application

B．transport

C．link

D．network

A.Layer two

B.Layer four

C.Layer one

D.Layer three

A.Layer 1

B.Layer 4

C.Layer 5

D.Layer 7

A.Layer 1

B.Layer 3

C.Layer 4

D.Layer 5

Which layer-function is mostly implemented in a network adapter（）。

A.Physical layer and link layer

B.Network layer and transport layer

C.Physical layer and network layer

D.Transport layer and application layer

●LANs can be connected by using bridges，which operate in the (67) .

(67) A．data-link layer

B．Physical layer

C．network layer

D．transport layer

A.data link layer

B.application layer

C.access layer

D.session layer

E.network layer

A.Layer 1

B.Layer 2

C.Layer 6

D.Layer 7

A.Layer 1

B.Layer 5

C.Layer 6

D.Layer 7