等差数列{an}的前n项和为Sn,a2+a8+a11=30,那么S13值的是[ ]
A.130
B.65
C.70
D.以上都不对
答案:A
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.
(75)处填()。
A.correspondent
B.comparable
C.similar
D.analogous
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