一物体从H处自由落下，经时间t落地，则当他下落t/2时刻，离地的高度为（   ）

下表是关于动物类群的描述，请你补充完整：

根据短文理解, 从A、B、C、D四个选项中选择正确答案填空。

    Mr. Smith 1 from London. Now he is in China. He is 2. He teaches 3 a middle school. He works very hard. His students like 4 very much. He can 5 a little Chinese. His students often teaches him Chinese 6 Sundays. Mr. Smith likes playing football. He often plays football 7 his students.

    Mr. Smith 8 a son. His name is Jack. He is student. He studies in a middle school. He goes to school 9 bike everyday. He gets back home at four in the afternoon. He likes 10 TV in the evening.