A、Demand a prompt response. B、Provide all the details. . C、Send it by express mail. D、Stick to the point. D短文在最后部分提到如何写投诉信，指出投诉信

The way to complain is to act business-like and important. If your complaint is immediate, suppose you got the wrong order at a restaurant, make a polite but firm request to see the manager. When the manager comes, ask his or her name. And then state your problem and what you expect to have done about it. Be polite! Shouting or acting rude will get you nowhere. But also be firm in making your complaint. Besides, act important. This doesn’t mean to put on airs and say "do you know who I am?" What it means is that people are often treated the way they expect to be treated. If you act like someone who expects a fair request to be granted, chances are it will be granted. The worst way to complain is over the telephone. You are speaking to a voice coming from someone you cannot see. So you can’t tell how the person on the line is reacting. It is easy for that person to give you the run-around. Complaining in person or by letter is generally more effective. If your complaint does not require an immediate response, it often helps to complain by letter. If you have an appliance that doesn’t work, send a letter to the store that sold it. Be business-like and stick to the point. Don’t spend a paragraph on how your uncle John tried to fix the problem and couldn’t.
20. What does the speaker suggest you do when you are not served properly at a restaurant?
21. Why does the speaker say the worst way to complain is over the telephone?
22. What should you do if you make a complaint by letter?