光盘上的光道是螺旋形的而不是同心圆。
（） may be fitted for operating the derrick topping lift (the wire which adjusts the derrick height). ["A capstan","A hold","A warp end","A mooring drum"]
功能化和复合化的有机高分子材料目前主要有几类？
模具的耐用度与哪些因素有关？
（） provides the head or pressure to supply the domestic water where required. ["The compressed air","The compressing air","The transfer pump","The head tank"]
压力机安全栓、安全插头是怎样起到安全保护作用的？
