THE NATIONAL FLAG
It is the duty of every citizen to honor the national flag. Why? Because the national flag is the symbol of a (the) country. To respect it means to respect the country. In other words, if a man loves his country, he must love the national flag.
In school, the national flag is usually raised at a certain time every day. Then the principal, teachers, staff and students are to (must) stand before it and sing the national anthem. It is indeed extremely meaningful to attend such a ceremony.