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当前学科：继电保护工考试
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并联电抗器的电阻R极小，略去不计，其数学模型为（）。
A .
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信息安全经理了三个发展阶段，包括（）.
当电动机运行时突然供电线路失电，为了防止线路恢复供电后电动机自行起动，要求电机起停控制线路应具有（）功能。
额定电压为开关设备所在系统的最高电压上限。标准值：3.6，7.2，10，24，35。
预测性消息写作应注意：（）、他人预测、权威预测、深度预测、审慎发稿。
电工作业人员对配电设备设施应定期进行（）巡视检查，认真做好各项运行管理记录，包括设备巡视检查记录、设备检修记录、工具检测记录、运行分析记录、值班记录等。
呼吸阀的作用，下列叙述不正确的是（）。
Drug Overuse ① Nowadays,millions of people misuse and even overuse pain medications and other drugs. Research by the American National Institute on Drug Abuse （NIDA， 1999） shows that around 2% of the population over age 12 were using drugs non-medically. ② NIDA views medications as a powerful force for good in the contemporary world. They reduce and remove pain for millions of people suffering from illness and disease. They make it possible for doctors to perform complicated surgery to save lives. Many people afflicted by serious medical conditions are able to control their symptoms and become active， contributing citizens. NIDA points out that most individuals who take these drags use them in a responsible. ③ Nevertheless， overuse of drugs such as opioids， central nervous system（CNS） depressants and stimulants does lead to harmful reliance in some people and is therefore becoming a serious public health concern. Although this abuse affects many people worldwide， particular trends of concern to the medical profession in the US appear among older adults， teenagers arid women. ④ Though it may be a surprise to many， the misuse of medications may be the most common form of drug abuse among the elderly. Dr Kenneth Schrader of Duke University， North Carolina states that although the elderly represent about 13% of the US population， those aged 65 and over account for the consumption of one third of all drugs. People in this age group use medications roughly three times more than the general population and have poorer compliance with instruction for use. In another study of elderly patients admitted to treatment programs， 70% were women who had overused medicines. ⑤ Unfortunately， this trend among women does not only affect those aged over. In general， among women and men who are using either an anti-anxiety drug or a sedative， women are twice as likely to become addicted. In addition， statistics compiled for 12 —17 year olds show that teenage girls are more likely than teenage boys to begin overusing psychotherapeutic medication such as painkillers， tranquillizers， stimulants and sedatives. Paragraph①（）. Paragraph②（）. Paragraph③（）. Paragraph④（）. Paragraph⑤（）. Medications kill pain for people suffering（）. Some people use medications about a couple of times more than the average people but with less compliance with（）. Another study researches some people， of which 70% of women had（）. Teenage girls are more likely than（）to begin psychotherapeutic medication overusing. Among women and men who are using either an anti-anxiety drug or a sedative， the former are twice as likely to（）.
简述羊水的主要来源。
原料粒度比是指（）。
某施工单位承揽了一项综合办公楼的总承包工程，在施工过程中发生了如下事件。 事件1：施工单位与某材料供应商所签订的材料供应合同中未明确材料的供应时间。急需材料时，施工单位要求材料供应商马上将所需材料运抵施工现场，遭到材料供应商的拒绝。两天后才将材料运到施工现场。 事件2：某设备供应商由于进行设备调试，超过合同约定的期限交付施工单位订购的设备，恰好此时该设备的价格下降，施工单位按下降后的价格支付给设备供应商，设备供应商要以原价执行，双方产生争执。 事件3：施工单位与某施工机械租赁公司签订的租赁合同约定的期限已到，施工单位将租赁的机械交还租赁公司并交付租赁费，此时，双方签订的合同终止。 事件4：该施工单位与某分包单位所签订的合同中明确规定要降低分包工程的质量，从而减少分包单位的合同价款，为施工单位创造更高的利润。 在什么情况下可导致合同无效？