分类：教育/科学-外语学习-英语考试
问题：急急急！请教一个问题！“以...为周期”英语怎么说？主要是介词用 
“以...为周期”怎么说？主要是介词用哪一个？
回答：1.once every...(time duration)/every(time period)
e.g.The Earth rotates once every 24 hours.
2.at regular intervals of (time period)
e.g. He went to the hoapital at regular intervals of two weeks.

Hope to be helpful.