Computer games are more and more popular with teenagers. Games are fun. After hours of homework it's great to relax by playing a game. But do games ever do kidsany harm? And are there any ways parents can help kids stay away from bad games? US researches are trying to find answers to these questions. One problem found that parents are not taking enough notice of their kids'games -playinghabits. Many games sells output controls   on the games to help parents make sure that children don't play things unsuitable for them, said David Walsh, president of the national Institute on media and the Family. Parents need to watch the games kids are playing and how much time they are spending playing them. The study found that playing games too long can affect kids' health as well as their schoolwork. Almost half of all " heavy games" are six to 17 years old. These kids are more likely to have weight and eyesight problems than other kids. Playing too many games also affects(v)how children do in school. Kids can ask their parents to set a time limit for playing games and remind them when the time is up. Don't forget to tell your parents about it. Nearly 50% of all "heavy games " are   _  .
seven to 17 years old six to 17 years old 17 years old six years old