下列属于概率抽样的方法是()
A.分层抽样
B.定额抽样
C.偶遇抽样
D.立意抽样
E.雪球抽样
参考答案:A
----Where is my watch? I can’t find it.
----Don’t worry. It must be ______ in your room.
A.somewhere
B.anywhere
C.everywhere
D.nowhere
母管制锅炉启动并列对汽压的要求,中压锅炉低于母管0.05—0.1MPa,高压锅炉一般低于母管0.2—0.3MPa,以防止并列后汽压急骤下降。