长期半卧位的MODS患者，哪一部位最易引起皮肤溃疡（） ["背部","骶尾部","踝部","枕后部","足跟部"]
若患者出现黑便，则消化道每日出血量至少（） ["10ml","20ml","30ml","50ml","100ml"]
尿毒症患者特征性表现是（） ["恶心呕吐","手足搐搦","呼气有氨味","心包摩擦音","鼻衄"]
能起到治疗作用的氧浓度不能低于（） ["21%","30%","25%","35%","45%"]
胃大部切除术，行胃空肠吻合，吻合口大小宜为（） ["1～2cm","2～3cm","3～4cm","4～5cm","5～6cm"]
简述PLC的主要功能。
