frequency 
英 [ˈfriːkwənsɪ]  美 [ˈfrikwənsi] 
n. 发生率，频繁，频率

例句：
We are concerned at the high frequency of racial attacks in the district. 

我们关心的是这个地区高频率的种族攻击。

The tanks broke down with increasing frequency. 

坦克故障越来越频繁。

Serious disasters appear to be increasing in frequency. 

重大灾害的发生越发频繁。

You can't hear waves of such a high frequency. 

你无法听到如此高频的声波。