数控机床导轨部件通常采用滚动导轨、塑料导轨、（）等，以减少摩擦力，使其在低速运动时无现象。
参考答案：静压导轨、爬行
记忆合金的主要成分是_______，它独有的物理特性是：_____________________________________________________．
– Why did they help Mrs Brown with her work?
– Because she was _____.
A．an old friend of them
B．the friend of them
C．on the their friend
D．a good friend of theirs
