In data communication, data link is those parts of two data terminal equipments that are controlled by a protocol along with the (71) data circuit, which together enable data (72) . So-called protocol means, in short, a set of rules that determines the behavior of functional units in achieving communication.

Data circuit, however, consists of a pair of (73) transmission channels that provides a means of two-way data transmission. Between data switching exchanges, the data circuit may or may not include data circuit-terminating equipment (DCE), depending on the type of (74) used at the data switching exchange. Between a data station and a data switching exchange or data concentrator, the data circuit includes the DCE at the data station end, and may include equipment (75) to a DCE at the data switching exchange or dam concentrator location.

（73）处填（）。

A．dependent

B．conformable

C．consistent

D．associated

确诊慢性胃炎的主要依据是

A．年龄

B．X线钡餐检查

C．大便潜血试验

D．HP检查

E．胃镜及胃黏膜活检