____ hearing the news that ShenzhouⅧ was sent into space, we shouted _____ joy. [ ]

A. At; by          

B. At; with

C. On; by  

D. On; with

共振倍率是指的（）。

A.叶片固有频率

B.激振力频率

C.叶片固有频率与激振力频率的比值

D.激振力频率与叶片固有频率的比值