a boatswain's mate的用法和样例：
- The first mate was studying to become a master.
- At thirty, he signed on as first mate with a cargo ship.
- He is looking for a wife but he hasn't found his ideal mate.
- There is a vein of melancholy in his character.
- There was a long lag in forwarding mail to us.
- A bowl of hot chicken soup is good for you.