阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用括号中词语的正确形式填空。

Tony is running now. He is in hurry because he can't find his backpack. He remembers (put) it under a tree beside the playground. He often (play) soccer on the playground.  His homework (be) in the backpack. His friends look it everywhere with him, they can't find it. are Tony and his friends now? They are at the lost and (find) office. Guess what? They see three backpacks here and one of them is (he). They are very glad because they are quite (luck).