Halloween is a very popular holiday in North America. People celebrate it on October 31st. On this day, many people decorate their houses. Many people like to make jack-o'-lanterns. They are made from pumpkins. Some jack-o'-lanterns are funny and some are scary!

    Children wear costumes and go trick-or-treating to collect candy. Many of these costumes are scary! Witch, ghost, vampire and black cat costumes are popular.

某同学用显微镜观察玻片标本时，发现视野中有污点存在，移动玻片时污点不动，换上高倍物镜，污点仍存在，那么污点在（  ）