（）或基频代表了机器的（）频率项。
参考答案：工频 ;旋转
Even though it is at least 20 years _____ we got to know, I can’t forget the scene_____ we were introduced to each other.
A．that , where
B．when, in which
C．since , when
D．since, where
8. To get the project started, _____ they need is some money.
A．only what
B．all that
C．all what
D．Whatever
