单项选择题 下列哪种用物是为昏迷病人进行口腔护理时必须准备的A．开口器B．食醋C．石蜡油D．溃疡散E．吸水管

单项选择题 应力单元体如图所示,则其三个主应力和最大切应力分别为(  )

单项选择题 The chemical shifts of the marked hydrogen nuclei in the following compounds should be： A、a :1.5~2.0 ppm, b amd c : 1.8~3.0 ppm, d : 9.0~10.0 ppm; B、a :1.5~2.0 ppm, b amd c : 5.5~7.5 ppm, d : 10.0~15.0 ppm; C、a :0~1 ppm, b amd c : 5.5~7.5 ppm, d : 9.0~10.0 ppm; D、a :1.5~2.0 ppm, b amd c : 5.5~7.5 ppm, d : 9.0~10.0 ppm.