Nowadays, the police have been applying the new regulation concerning the use of seat belts. In European countries, this regulation has been applied for a long time. However, this new regulation has become controversial and is an interesting topic to discuss. Here are some of the arguments. The use of seat belts has been proven to reduce the risk of injury or death in an accident. Seat belt has become standard component in cars. The research shows that most car accident will cause an injury to the head. Frequently, drivers or the passengers driving without seat belts die because of this. By wearing the seat belts, the injury will not happen since belts restrain our body on the car seat when the accident happens. Unfortunately, many cars, especially the old ones, don't have seat belts. This is because the traffic conditions in the past were unlike the recent traffic conditions. The designer of old cars didn't consider a seat belt as an important part. Besides, the drivers wearing the seat belt will think that they are completely safe, so they may drive carelessly. They are safe, indeed, but how about safety of other? The seat belt is only one of the ways to reduce the risk of car accidents. It doesn't mean that we are completely safe In short, our safety depends on ourselves. "... that they are completely safe." (Paragraph 3) What does the word 'they' refer to?

Question

Nowadays, the police have been applying the new regulation concerning the use of seat belts. In European countries, this regulation has been applied for a long time. However, this new regulation has become controversial and is an interesting topic to discuss. Here are some of the arguments.

The use of seat belts has been proven to reduce the risk of injury or death in an accident. Seat belt has become standard component in cars. The research shows that most car accident will cause an injury to the head. Frequently, drivers or the passengers driving without seat belts die because of this. By wearing the seat belts, the injury will not happen since belts restrain our body on the car seat when the accident happens.

Unfortunately, many cars, especially the old ones, don't have seat belts. This is because the traffic conditions in the past were unlike the recent traffic conditions. The designer of old cars didn't consider a seat belt as an important part. Besides, the drivers wearing the seat belt will think that they are completely safe, so they may drive carelessly. They are safe, indeed, but how about safety of other?

The seat belt is only one of the ways to reduce the risk of car accidents. It doesn't mean that we are completely safe In short, our safety depends on ourselves.

"... that they are completely safe." (Paragraph 3) What does the word 'they' refer to?