据统计，两宋时期每一劳动力平均单位产量为1020斤，而11—13世纪的英国，这一数据仅为239斤。这从一个侧面反映了

A．英国推行圈地运动导致了农业生产落后

B．重农抑商比重商主义更有利于农业发展

C．宋代冶铁技术的改进促使了亩产量提高

D．古代中国的农业文明一度处于领先地位

A transport layer protocol has several responsibilities. One is to create a process-to-process (program-to-program) communication, TCP uses port (1) to accomplish this. Another responsibility of a transport layer protocolis to create a  (2) and error-control mechanism at the transport level. TCP uses a sliding(3) protocol to achieve flow control. It uses the acknowledgment packet, time-out, and retransmission to achieve(4) control. The transport layer is also responsible for providing a connection mechanism for the application program. The application program sends  (5) 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.

空白（1）处应选择（）

A.numbers

B.connections

C.diagrams

D.resources