用所给单词的适当形式填空，未提供单词的限填一词
Last month, Jack went to swim in the sea. He swam really far, past the rocks and out to sea. He enjoyed ____(he)swimming in the blue sea.
Then he saw something ____(move) towards him. It was huge and gray, ____a large fin. It was a shark! ____shark started to swim around him. Jack began to swim back, ____the beach was too far away.
Jack was really scared. Suddenly another creature appeared next to him in the water. It was a dolphin! It pushed him away from the shark. Jack sat____ its back as it swam towards the beach.
Soon they were near the beach. The shark did not follow them. As soon as Jack ____ (step) onto the beach, the dolphin swam away. He will always remember how this ____ (friend) animal saved his life.
This is not just a story. In fact, dolphins do save people's ____(life)like that. There are also many dangerous things in the sea, so take ____(careful)when you go swimming.
