根据短文理解，从A、B、C、D四个选项中选择最佳答案填空。

       Jimmy lives in London and he began to swim a few months ago. He 1 swimming, and he often goes to the swimming pool near his 2 with his mother and swims there for 3 or two.

       One day his mother said, “You 4 quite well now. And you want to see the sea, don't you? Your father and I are going to 5 you there on Sunday, and you are going to swim in the  6. It's not cold now, and it's much nicer than a swimming pool.”

      Jimmy's parents took him 7 the sea by their car on Sunday. They 8 at the side of a small harbor (港口）. Jimmy got out and   9 the sea for a long time, but he was not very 10. Then he asked his mother,“ Which is the shallow (浅的）end (部分）?”