a letter of congratulation的用法和样例：
- She was chosen to present a letter of congratulation to the crew.
- He sent her a letter of congratulation on her passing the exam.
- To write a letter of congratulation is one of the best ways to promote good will.
- I'm writing a letter of thanks to them.
- A good face is a letter of recommendation.
- He is fishing for information by a letter of inquiry.