填土施工采用平碾时的分层厚度为（）mm ["100~150","150~200","200~250","250~300"]
真空槽内残余压力为2700pa时，真空槽内钢水到槽底的距离（）m。 ["0.25","0.34","0.37","0.38"]
铸铁和钢材相比，优点有（）。 ["减磨性好","耐磨性低","消振性","低的缺口敏感性"]
真空槽内残余压力为67pa时，真空槽内钢水到槽底的距离（）m。 ["0.25","0.34","0.37","0.38"]
真空槽内残余压力为35000pa时，进入真空槽内钢水的重量（）t。 ["0","1.69","3.14","4.56"]
简述影响睡眠的因素有哪些。
