当挖土深度超过()或发现有地下水以及土质发生特殊变化等情况时,应根据土的实际性能计算其稳定性,以确定边坡坡度或采取其他防护方案。 ["5米","4米","3米"]
塑料尺经过毛皮的摩擦可以吸起小纸屑,是因为尺子上有什么的存在?() ["水分","磁力","静电","粘性"]
砂糖溶液的黏度随着浓度之增高而() ["降低","不变","提高","比一定"]
硬水是指含有高浓度矿物质的水,尤其是指含有镁和哪种元素?() ["氧","铁","钙","碳"]
利用低温来储藏食品的方法是() ["浓缩","干燥","冷冻","混合"]
什么叫氯差?控制氯差的意义?