陶渊明为什么在这篇文章中虚构了一个与黑暗现实社会相对立的美好境界?
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医疗机构所需全血及其血液成分,需要那级政府批准的血站负责提供?()
A. 省级以上人民政府卫生行政部门批准
B. 由各医院批准
C. 医疗机构自采自用
D. 血站
E. 以上都不正确
Select valid reasons for IT performance issues that cannot be universally solved by adding more hardware:()
A. adding hardware may exacerbate inefficiency, which can lead to over provisioning and lower utilization
B. performance may degrade due to bottlenecks such as database connections that won’t scale in lock step with other dimensions such as computing capacity or memory
C. both A and B are valid
D. neither A nor B are valid
调车信号XJJ1-2线圈在进路预先锁闭时有一条脱离8线网络的自闭电路,所以,当进路中某区段故障时信号不关闭。
A. 正确
B. 错误
对高收入人群进行研究,一般先找到几个高收入者,然后通过他们的介绍找到新的高收入者,这种抽样方法是()
A. 雪球抽样
B. 配额抽样
C. 判断抽样
D. 方便抽样