琼脂糖凝胶电泳通常采用的装置是（）

A.柱装装置

B.水平装置

C.管状装置

D.垂直装置

E.旋转装置

A transport layer protocol has several responsibilities, One is to create a process-to-process (program-to-program) communication; TCP uses port (11) to accomplish this. Another responsibility of a transport layer protocol is to create a (12) and error-control mechanism at the transport level．TCP uses a sliding (13) protocol to achieve flow control．It uses the acknowledgment packet，time-out，and retransmission to achieve (14) control．The transport layer is also responsible for providing a connection mechanism for the application program．The application program sends (15) of data to the transport layer．It is the responsibility of the transport layer at the sending station to make a connection with the receiver．

A．packet

B．time

C．error

D．phase