矿物基液压油通常染成的颜色为：（）.
A.紫色
B.蓝色
C.绿色
D.红色
参考答案：D
在凭证处理中，未经复核的凭证可随时修改。( )
To learn to swim well, ___________.
A．one needs much practice
B．much practice is needed
C．much practice needs
D．one is needed much practice
