And once each month, mail would arrive in California after a slow trip by wagon from Saint Louis,Missouri.

VOA: special.2009.05.28

So after about a month, I started to, once in a while, experience some envy toward David.

一个月后，我开始偶尔，对David产生一种嫉妒。

哈佛公开课 - 幸福课课程节选

Once a month, people come together at a restaurant in Washington to listen to several storytellers perform.

VOA: special.2009.03.27

Security consultants say a foreigner gets kidnapped, on average,once every other month in the country, with ransom payments for their release reaching hundreds of thousands of dollars.

VOA: standard.2009.09.10