A、By making laws. B、By enforcing discipline. C、By educating the public. D、By holding ceremonies. A

Laws have been written to govern the use of the American National Flag, and to ensure proper respect for the flag. Custom has also governed the common practice in regard to its use. All the armed services have precise regulations on how to display the national flag. This may vary somewhat from the general rules. The national flag should be raised and lowered by hand. Do not raise the flag while it is folded. Unfold the flag first, and then hoist it quickly to the top of the flagpole. Lower it slowly and with dignity. Place no objects on or over the flag. Do not use the flag as part of a costume or athletic uniform. Do not print it upon cushions, handkerchiefs, paper napkins or boxes. A federal law provides that the trademark cannot be registered if it comprises the flag, coat of arms, or badges of the United States. When the flag is used in unveiling a statue or monument, it shouldn’t serve as a covering of the object to be unveiled. If it is displayed on such occasions, do not allow the flag to fall to the ground, but let it be carried high up in the air to form a feature of the ceremony. Take every precaution to prevent the flag from becoming soiled. It should not be allowed to touch the ground or floor, nor to brush against objects.
Questions 19 to 22 are based on the passage you have just heard.
19. How do Americans ensure proper respect for the national flag?
20. What is the regulation regarding the raising of the American National Flag?
21. How should the American National Flag be displayed at an unveiling ceremony?
22. What do we learn about the use of the American National Flag?