a red-light district的用法和样例：
- Don't go there! It is a red light district.
- A red light is usually a signal of danger.
- Enjoy your weekend in this city but be careful in the red light district!
- The two old lady complains that their hotel is in the red light district of Frankfurt.
- The car was fetched up short by a red light.
- Send out a red light on all unnecessary expenses.