frequency of sampling

例句：

1. 1.The frequency of occurrence is low.
   发生的频率很低。
2. 2.The frequency of this event has increased over the past year.
   这个事件的发生频率在过去的一年里有所增加。
3. 3. The frequency of traffic accidents has decreased significantly.
   交通事故的发生频率已经显著下降。