a merchant seaman的用法和样例：
- Harry has kicked around all over the world as a merchant seaman.
- John's father was a merchant seaman and John did not see a lot of his father when he was small.As a child, John was a prankster and he enjoyed getting in trouble.
- A book in which a merchant records credit sales.
- He became afterward a merchant of great note.
- The scout disguised himself as a merchant.