In the following essay, each blank has four choices. Choose the most suitable one from the four choices and write down in the answer sheet.

A socket is basically an end point of a communication link between two applications. Sockets that extend over a network connect two or more applications running on (31) computers attached to the net-work. A socket (32) two addresses: (33) . Sockets provide a (34) communication channel between one or more systems. There are (35) sockets separately using TCP and UDP.

（34）是（）

A.full-duplex

B.half-duplex

C.simplex

D.complex