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问题 单项选择题

大黄和虎杖均具有的功效是( )

A．活血，通便，解毒，止咳

B．活血，利湿，解毒，止痛

C．活血，止痛，止痉，解毒

D．活血，通便，利湿，止血

E．活血，解毒，通便，退黄

答案

参考答案：E

填空题

（1）在粗制CuSO4·5H2O晶体中常含有杂质Fe2+。在提纯时为了除去Fe2+，常加入合适氧化剂，使Fe2+氧化为Fe3+，下列物质可采用的是__________。

A. KMnO4      　 B. H2O2   　　  C. Cl2水  　　    D. HNO3    

然后再加入适当物质调整至溶液pH=4，使Fe3+转化为Fe(OH)3，可以达到除去Fe3+而不损失

CuSO4的目的，调整溶液pH可选用下列中的_______。

A. NaOH    B. NH3·H2O    C. CuO    D. Cu(OH)2

（2）甲同学怀疑调整至溶液pH=4是否能达到除去Fe3+而不损失Cu2+的目的，乙同学认为可以通过计算确定，他查阅有关资料得到如下数据，常温下Fe(OH)3的溶度积Ksp=8.0×10-38，Cu(OH)2的溶度积Ksp=3.0×10-20，通常认为残留在溶液中的离子浓度小于1×10-5 mol/L时就认为沉淀完全，设溶液中CuSO4的浓度为3.0 mol/L，则Cu(OH)2开始沉淀时溶液的pH为_____，Fe3+完全沉淀时溶液的pH为_______，通过计算确定上述方案_______ （填“可行”或“不可行”）。（已知：lg2=0.3；lg5=0.7）

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单项选择题

The usual way to ensure reliable delivery is to provide the (71) with some feedback about what is happening at the other end of the line. Typically, the protocol calls for the receiver to send back special (72) frame bearing positive or negative (73) about the incoming frames. If the sender receives a positive acknowledgement about a frame, it knows the the frame has arrived safely. On the other hand, a negative acknowledgement means that something has gone wrong, and the frame must be transmitted again.
An additional complication comes from the possibility that hardware troubles may cause a frame to (74) completely. In this case, the receiver will not react at all, since it has no any reason to react. It should be clear that a protocol in which the sender transmits a frame and then waits for an acknowledgement, positive or negative, will hang forever if a frame is ever lost due to, for example, (75) hardwareo

A．data

B．control

C．request

D．session
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