下列各项在我国古代出现的先后顺序是
①使用骨针缝衣 ②采用天然火 ③制黑陶和白陶 ④用麻线织布 [ ]
A.①②③④
B.②③④①
C.①②④③
D.②①④③
答案:D
煤矿对供电的基本要求是供电可靠、()、技术合理、()。
What does the term head mean when applied to a fire pump?()
A.Length of the discharge pipe
B.Height of the discharge pipe
C.Difference between the discharge and suction pressures
D.Sum of discharge and suction pressures