Last night, a friend who is a primary school teacher, asked me what is Facebook. When I wanted to explain to her, my F3 son started to talk about. I never know he knows Facebook. At the same time, my son then told me he can classify all his teachers into three categories. 1. Speak all the time, do not like student talk and discuss 2. Like to ask questions, or telling jokes, however, most of time talking by oneself and don't let students answer. And the jokes are in fact not so good. 3. Really engage students to talk and discuss. Interesting.