阅读下面短文，掌握其大意，从每题所给的A、B、C、D项中，选出最佳选项。 Laughter is natural for people. We start to laugh at about four months of age. We start to laugh even1 we start to speak.
Laughter connects us with others. We laugh more when we are with other people. It's difficult to pretend to laugh. Laughter is2. When people pretend to laugh, most people know it's not real.
When do people laugh?
Only 10 to 20 percent of laughter is about something3. Most laughter is about being friendly with other people. Most laughter says, "I don't want to4 with you. I want to be friendly with you." This kind of laughter brings people together.
We often laugh when we feel nervous. In movies, there is often a joke at an exciting moment when everyone feels nervous. It is usually a(n)5 joke, but we laugh a lot. Our laughter helps us6.
Why doesn't everyone laugh at the same joke?
Not everyone has the same sense of7. Some people think a joke is funny, but other people don't think so. People have different ideas about what is funny.
Our idea of what is funny changes with8. For young children, the world is new. They are interested in many things, so they laugh9. Teenagers often laugh to protect themselves. Adults laugh at themselves and other people with similar problems. They laugh at things that give them stress. Our10 for laughter change gradually.
