单选题 .  Different countries and different races have different manners. Before entering a house in some Asian countries, it is good manners to take off your shoes. In European countries, even though shoes sometimes become very muddy, this is not done. A guest in a Chinese house sometimes does not finish a drink. He leaves a little, to show that he has had enough. In a Malay house, too, a guest always leaves a little food. In England, a guest always finishes a drink to show that he enjoys it.
    We should like to find out the customs of other races, so that they will not think us ill-mannered. And people all over the world agree that being well-mannered really means being kind and helping others, especially those older or weaker than themselves. If you remember this, you will not go very far wrong.
    Here are some examples of the things that a well-mannered person does or does not do.
    He never laughs at people when they are in trouble. He is always kind either to people or to animals. When people are waiting for a bus, or in a post office, he lines up to wait his turn. In the bus, he gives his seat to an older person or a lady who is standing, ff he accidentally bumps into(碰撞) someone, or gets in their way, he says "Excuse me" or "I'm sorry".
    He says "Please" when making a request, and "Thank you" when he receives something. He stands up when speaking to a lady or an older person, and he does not sit down until the other person is seated. He does not talk too much about himself. When eating, he does not speak with his mouth full of food.1.  According to the passage, a knowledge of the customs of other races ______.