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.来源：www.examda.com

2.生理原则：
体育课：
Encouraging physical activity in the young through compulsory PE fights child obesity and contributes to forming lifelong habits of exercise.
体罚：
The actual physical damage inflicted via corporal punishment on children can be horrifying.
Some parents lose control and can injure children - even breaking bones or causing bruises.
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.来源：www.examda.com

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, aggression, crimes and wars are broadcast through the daily news as well as in movies, showing dark pictures that encourage psychological tension, pessimism 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 breakdowns 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 humiliated and lose self-respect.
A physical punishment is likely to provoke resentment and further misbehavior.
课外活动：
Without the opportunity to do this, they could grow up immature 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 relevance, then they will soon get tired of studying altogether, which is the last thing parents would want.
抽烟：
First, smoking undoubtedly 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 deterrent to criminal behaviour.
People may feel safer when they see armed police, especially if they perceive them as a response to a heightened risk.来源：www.examda.com