被审计单位在经营方面存在的可能导致对持续经营假设产生重大疑虑的事项或情况主要包括（）

A、财务经理甲离职，已经重新聘请一位财务经理乙上任

B、出现用工困难

C、失去主要市场、特许经营权或主要供应商

D、遭遇自然灾害

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