旁听生

例句：

1. 1. The professor noticed that some students were sitting in the back row on the side.
   教授注意到有些学生坐在后排的边上。
2. 2. The extra student was allowed to join the class for a few minutes.
   这个额外的学生被允许加入课程几分钟。
3. 3. The visitor was given a tour of the museum and asked to observe the exhibits.
   访客被安排参观了博物馆并观察展品。