下面对生态系统的叙述，不正确的是：

A．分解者对生态系统的物质循环起重要作用

B．在稳定的生态系统中，各种生物的数量总是维持不变的

C．植物作为生产者，参与了生态系统的物质循坏

D．生态系统中，生产者、消费者、分解者缺一不可

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 protocol is 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（2）处应选择（）

A.procedure

B.function

C.route

D.flow