阅读下列短文，从A、B、C三个选项中选出一个能正确填入相应空格内的最佳答案。
Mr. White wanted to spend a day at the beach. He 1 his daughter Nancy and her two friends, Helen and Karina. They all went to Ocean Beach in New Zealand.
The group swam and surfed. Then they saw something 2. "They are large fins (鱼鳍)," said Mr. White.
The 3 saw seven dolphins moving towards them. The dolphins were worried. They 4 the water with theft mils(尾巴). They kept moving around the swimmers. Then one large dolphin swam towards Mr. White and Helen. Next, it dived down underwater. Mr. White saw something grey moving in the 5.
A shark 6 underwater. It wasn't far from the people. Now the shark was not slow. It moved 7! So the dolphins used their 8 to swim even faster. Each one splashed (飞溅) its tail even more. Then Mr. White knew the dolphins didn't want to 9 him and the girls. These sea mammals (哺乳动物) wanted to keep them safe.
The dolphins stayed close to the group until the shark 10. When Mr. White and the kids were safe, the dolphins swam away. "You want to say thank you and shake their flippers." Mr. White said. "These dolphins are heroes."
