用括号内所给动词的适当形式填空，可加助动词或情态动词。

    It was getting dark. Some children and two Canadian women were still skating near a big hotel. They ____ (have) a great time.

    “A boy said to his friends,”I ____ (not skate) on a real lake so far. It's wonderful! Look! I ____ (fly)!" Suddenly the ice broke. One of the boys fell into the river. The children shouted, "Help! Help!" They didn't know what they  ____ (do). The two Canadian friends heard them and skated over to help the boy.

    The ice were not thin enough. The two Canadians fell into the river too. But they tried their best ____ (save) the little boy. They knew they were quick, or the boy would be frozen.

    Many guests from the hotel came over and ____ (run) to help. The boy and the two Canadian women were out of water at last. One of the women ____ (not feel) well. She ____ (send) to hospital at once. She felt happy because the boy was safe.

⊙O的半径为6，点P在⊙O内，则OP的长可能是（  ）