—To say is one thing, but to do is quite _________.

—Yes, it is true. Thanks!

A．other

B．the other

C．others

D．another

两渐开线齿轮传动时（）。

A.传动比瞬间不等

B.平均传动比不等

C.传动比是恒定的

D.传动比瞬间不等，平均传动比相等