硅芯管由高密度聚乙烯（HDPE）外壁、可能有的外层色条和永久性固体硅质（）层组成的单孔塑料管。
参考答案：内润滑
— ____make she different from the othe rstudents?
—Honesty,Ithink.
A．How is it that
B．How is that
C．What is it that
D．What it is that
陇海线与京广线的铁路枢纽是[ ]
A、石家庄
B、郑州
C、武汉
D、广州
