在括号中填上合适的词语。

____的掌声      ____的声音          ____的节日            ____的人群

____的队员      ____的检阅           ____的队伍           ____的儿童

       In Zhangdian High School, Wuhan City, teachers and students often see a man collecting trash.

       The man is Luo Yiming, a 54-year-old history teacher in the school. His wife is a dormitory supervisor. Their two sons have already grown up and are working.

       To ask students to save some things, take care of the environment and do good

 things, Mr. Luo has been collecting trash since 1997 in his free time. In order to store more trash, he even put the trash into his small room.

       He sells the trash and gets some money. But he doesn't keep the money himself but helps Students. In the past 16 years, with the money of over RMB 22,000,he helped more than 60 poor students. At the same time, he helped 5 poor villagers, too. After Wenchuan earthquake, Mr. Luo gave away RMB 2,000 to the quake area.

       "Mr. Luo's kindness influenced us greatly. We should all learn from him. " said Pan Hongmei , one of the students Mr. Luo helped.

       "Saving is a kind of generosity and giving is a kind of happiness. " said Mr. Zhong, the headmaster of the school , "Mr. Luo gives us a best example. "

在平行四边形ABCD中，AC与BD交于点O,E是线段OD的中点，AE的延长线与CD交于点F,若$\overrightarrow{AC}=\overrightarrow{a},\overrightarrow{BD}=\overrightarrow{b}$，则$\overrightarrow{AF}=$(   )