阅读下面短文，用括号内所给动词的适当形式填空（必要加助动词或情态动词）。 It was three o'clock. Robert and his friends (1) ______ (play) hide-and-seek (捉迷藏) in a neighbor's house. The game was very interesting and they (2) ______ (enjoy) it very much. Suddenly Robert had a good idea. He smiled to himself. This time he found a good place (3) ______ (hide) in. No one could (4) ______ (find) him! There was an old fridge in the kitchen. The neighbor (5)______ (not use) it for a long time. Robert opened the door and went in quietly. Of course, he (6) ______ (not find). But he was in great trouble! His friends forgot him and they all went home. His mother came to (7) ______ (get) him home, but he was lost. Everyone helped her (8) ______ (look) for Robert. But no one found him. The next morning, the neighbors (9)______ (hear) a knock in the kitchen. It (10)______ (seem) to come from the old fridge. They opened it and found Robert there! He was dead.