—Yes, when we cross the street we must wait ________ the traffic lights turn green.

(B)

    Thanksgiving Day is on the fourth Thursday of November in the U.S. and on the second Monday in October in Canada.

    For many Americans it is the most important (重要的) holiday apart from (除了) Christmas. Schools, offices and most businesses (商业) close for Thanksgiving, and many people make the whole (整个的) weekend a holiday.

    Today people celebrate Thanksgiving to remember the early days. The most important of the celebration is a traditional (传统的) dinner with foods that come from North America. The meal included (包括) turkey (火鸡), sweet potatoes and so on.

    On Thanksgiving there are special (特别的) TV shows and sports games. Thanksgiving is the beginning of Christmas period, and the next day many people go out to shop for Christmas gifts.

在探究凸透镜成像规律的实验中，我们发现（   ）

塞曼的经历对我们有什么启示？

点拨：许多人并不是没有理想，并不是没有潜力，但最终都碌碌无为，一事无成。其主要原因是不愿意吃苦，不能克制自己，不愿为了自己的长远利益而牺牲眼下的享乐。塞曼认识到了自己的弱点，并想办法克服它、战胜它，所以他就能自强，就能成功。