重点讲解：
1. used to do sth.
过去常常；过去曾做某事；
eg. We used to be good friends, but fell apart about a year ago.
我们过去曾经是好朋友，但一年前关系破裂了。
eg. John used to visit his parents once a week when he worked as an assistant in the city.
约翰在城里当服务员的时候，总是每周去看望父母一次。
2. stay up
深夜不睡；熬夜；
eg. People often do not sleep on the last day of year and stay up to welcome the new year. We call it pernoctating.
守岁，就是在旧年的最后一天夜里不睡觉，熬夜迎接新一年的到来。
eg. I hope you will not always stay up late, but form a good habit of early to bed, early to rise.
我希望你不要总是熬夜，要养成早睡早起的好习惯。
3. one by one
逐个地；依次地；
eg. Researchers, sometimes working more or less in teams, divide problems into small pieces and try out different solutions to them one by one.
有时候，研究人员或多或少地分组合作，把问题分解并且逐个找到相应的解决办法。
eg. All the applicants were interviewed one by one.
所有的申请者一个接着一个参加面试。
