a jewel called a pearl的用法和样例：
- With its long history, brilliant culture, picturesque landscape and rich resources, Sanmenxia, an ancient yet new city, has been called a pearl on the Yellow River.
- Virtue is a jewel of great price.
- She wears a pearl necklace today.
- A young swan is called a cygnet.
- I've decided to invest in a pearl necklace for my wife.