根据短文内容，完成下列各小题。

    It's four thirty in the afternoon. There are many students on the playground. Jim and his friends are playing basketball. Li Lei and other boys are playing football. Miss Gao is watching the games. She is looking after the clothes, too. Where are the girls? They are over there. Some are running, others are jumping. The twins are on duty today. They are in the classroom. Lucy is cleaning the window, Lily is sweeping the floor. They are working hard. They are tired(疲倦的) but happy.

我国每年春晚都会有不少少数民族的歌舞节目，既丰富了春晚内容，又让人们感受到少数民族的风采。这样有利于 （   ）
①贯彻民族团结原则  ②各民族经济发展  ③各民族文化共同繁荣  ④各民族融为一体   

凝固点是0℃，酒精的凝固点是-117℃，小明把酒精和水的混合物放入冰箱的冷冻室（冷冻室温度可达-5℃）中，经过相当长的时间后，从冷冻室取出混合液体时，却发现混合液没有凝固。就这个现象请你提出一个猜想：____ ；根据这一猜想举出一个实际应用的例子____ 。