单项选择题

某抽水蓄能电站总装机容量为1000MW，上池总库容为3200万m3，选定坝型为黏土斜墙坝，斜墙靠近上游，最大坝高50m。斜墙下游采用粗砂填筑，坝基为连续级配砂砾石，厚度约25m，为中等透水地基。砂砾石下部为弱风化花岗片麻岩，为微透水岩体。
根据已知的坝基砂砾石级配曲线，如图所示。计算满足可灌比的水泥黏土浆浆液材料的d85粒径。计算的d85最接近以下的哪一个值（　　）

A.0.2mm
B.0.15mm
C.0.12mm
D.0.08mm

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单项选择题

下列有关物质用途的说法错误的是（）

A.AgI可用于人工降雨
B.AgBr常用于制感光材料
C.Na2O2常用作呼吸面具和潜水艇里的供氧剂
D.BaCO3可代替BaSO4用作“钡餐”

单项选择题

In multipoint networks , there are tree persistence methods when a station finds a channel busy.in the 1-persistent method,after the station finds the line idle,it sends its frame immediately.this method has the （） chance of collision because two or more stations may find the line （） and send their frames immediately. In the nonpersistent method , a station that has a frame to send （） the line . If the line is idle , it sends immediately If the line is not idle , it waits a （） amount of time and then senses the line again.The nonpersistent approach （请作答此空） the chance of collision because it is unlikely that two or more stations will wait the same amount of time and retry to send simultaneously The p-persistent approach combines the advantages of the other two strategies . It reduces the chance of collision and improves efficiency.

A.increases
B.equalizes
C.reduces
D.cancels

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