The data station usually means a (71) unit that provides data for transmission, that accepts transmitted data, and that performs all functions necessary for communication with another functional unit. Data stations may be divided into two kinds, the primary stations and the secondary stations, (72) control functions.

In (73) data link control, the primary station is the data station that supports the primary control functions of the data link, generates commands to be transmitted, and interprets received responses. Specific responsibilities assigned to the primary station include initialization of control signal interchange, organization of data flow and actions regarding error control and error recovery functions. The secondary station executes data link control functions as (74) by the primary station, interprets received commands and (75) responses to be transmitted.

（75）处填（）。

A．produces

B．creates

C．generates

D．makes

下列哪种试剂能鉴别出硫酸、氢氧化钾和氯化钠三种无色稀溶液

A．石蕊试液

B．稀盐酸

C．氢氧化钠稀溶液

D．氯化钾溶液