导致脐带脱垂的原因有（）。①头盆不稳②先露入盆受阻③胎盘位置较低④脐带过长
A.①
B.①②
C.①②③
D.①②③④
参考答案：D
物流的主要功能要素包括运输、仓储、装卸、流通加工。
-_____ you ______ the magazine from the library yet?
-Yes. I _____ it for three days.
A．Have, borrowed; have kept
B．Have borrowed; have borrowed
C．Have , kept; have borrowed
D．Have, kept, have kept
