3)时间：
电视：
Nowadays many people spend the biggest part of their free time watching television.
兼职工作：
After-school jobs are bad for teenagers because they take time away from studying.
运动：
Sport is a waste of school time and resources.

2.生理原则：
体育课：
Encouraging physical activity in the young through compulsory¹ PE fights child obesity² and contributes to forming lifelong habits of exercise.
体罚：
The actual physical damage inflicted³ via corporal punishment on children can be horrifying⁴.
Some parents lose control and can injure children - even breaking bones or causing bruises⁵.
禁烟：
There is little doubt that smoking tobacco is extremely harmful to the smoker's health.
配枪：
Routinely arming police officers allows them to defend themselves.

3.心理原则
电视：
Depression is a well-known psychological problem of modern society. The popularity of TV watching is among the reasons of this phenomenon. Violence, aggression⁶, crimes and wars are broadcast through the daily news as well as in movies, showing dark pictures that encourage psychological tension, pessimism⁷ and negative emotions.
While TV and movies shouldn’t be a way to hide from life, sometimes it can help us to cope.
压力：
Some students have mental breakdowns⁸ and, in extreme cases, attempt suicide because they cannot handle the pressure.
体罚：
They learn that force is an acceptable factor in human interaction; they feel humiliated⁹ and lose self-respect.
A physical punishment is likely to provoke resentment¹⁰ and further misbehavior.
课外活动：
Without the opportunity to do this, they could grow up immature¹¹ and unformed.
Iit is also important to remember that children need to relax as well as work. If everything they do must have educational or academic relevance¹², then they will soon get tired of studying altogether, which is the last thing parents would want.
抽烟：
First, smoking undoubtedly¹³ helps many people to relax.
Indeed the more of a 'forbidden fruit' cigarettes become, the more attractive they will be to adolescents.( 逆反心理)
媒体：
Excessive * and violence in the media can lead to similar behaviour in viewers (studies in the USA have shown this).
Psychologists claim that television does not have a simple, direct stimulus-response effect on its audiences. (模仿心理)
配枪：
Routinely arming the police is an effective deterrent¹⁴ to criminal behaviour.
People may feel safer when they see armed police, especially if they perceive them as a response to a heightened risk.