语法填空

    July is coming. People all around the world are talking about their ____ (vacation). Parents would like ____ (help) their children relax. ____ (luck), they have two months off. Some people enjoy quiet life, so many of ____ (they) stay at home watching TV, using computers and so on. ____ some spend time differently. My pen pal Tony ____ blonde hair is a boy from the US. He says that ____ (America) like going to the countryside. Just like his big family, they often go to a farm. There, some can feed animals, some can play and ____ (other) can watch ____ nice sky and rivers. They can also taste delicious food. They are quite ____  (interest) in the life there.

 在“探究凸透镜成像规律”的实验中，各组使用相同焦距的凸透镜进行实验．
(1)小华所在的小组实验操作规范，测量准确，该小组实验记录如下表：

请你根据上表信息，求出凸透镜的焦距f=____ cm．
(2)小华所在的小组把蜡烛放在该凸透镜的焦点上，凸透镜固定不动，将光屏向远离凸透镜的方向移动的过程中，在光屏上观察到的现象是____ ．
(3)若烛焰、凸透镜、光屏放在适当位置时恰好在光屏上成清晰的像，当凸透镜位置不变，烛焰向远离凸透镜方向移动一小段距离时，为了在光屏上再成清晰的像，光屏应向____ (远离／靠近)凸透镜方向移动适当的距离．
(4)对于焦距相同的凸透镜，一个物距应该对应唯一的像距，但从各小组汇报数据中发现，物距均为12．00cm时，有三个小组所测像距分别为23．00cm、24．00cm、26．00cm．若他们的数据差别不是因为长度测量误差导致的，你认为出现这种情况的操作原因是____