1. 表示经常发生的、习惯性的动作，通常用usually, often, always, sometimes, every day, once a week等作时间状语。
I usually have my hair cut once a month. 我通常一个月剪一次头发。
The students often do their experiments in the lab. 学生们常常在实验室做实验。
He is always ready to help others. 他总是准备着帮助他人。
