Bowing is a very important custom in Japan. Unlike people in many other countries, they greet each other by bowing instead of shaking hands. It is impolite not to return a bow to whoever bows to you. Bowing has many functions in one. It expresses the feeling of respect, thanks, regret, and so on. You can bow when you say, "thank you", "sorry", "hello", "goodbye", "congratulations", "excuse me", "good morning", and more. Bowing seems simple, but there are different ways of bowing. Bowing techniques vary from a small nod of the head to a long, 90-degree bow. It depends on the social position or age of the person you bow to. If your opposite is of higher social position or older than yourself, you are supposed to bow deeper and longer than him or her. It is polite to bow from your waist. Men usually keep their hands at their sides, and women usually put their hands together on their legs with their fingers touching. If it is not a very formal situation, you can bow by nodding. The most common bow is a bow of about 15 degrees. You might feel strange doing it, but try to bow in Japan. You will be considered very polite! By saying "Bowing has many functions in one", the author means that   _  .
one kind of bow has many similar functions people can express different feelings by bowing people bow to express their feelings the more times you bow, the more respect you receive