In this game you are in a tank and the screen shows your outside view. You gain points by shooting enemy tanks, supertanks, missiles(导弹) and saucers(飞碟). Experts gain scores of around 150,000 points at this game. To get a high score you have to destroy twenty tanks as quickly as possible. After this the supertanks, missiles and saucers appear. These are worth far more points than the ordinary tanks. (The number of tanks you have to destroy before the supertanks appear is various on different machines. ) Try to get near an enemy tank from the side or back so it cannot shoot at you. Then when you get close, turn to it, line it up in your sights and fire before it turns to shoot at you. If your missiles are too slow, quickly get away by moving out of the enemy's line of life. You can then move around the enemy and come in from another side. When a supertank appears, try to destroy it. Then wait safely behind an obstacle(障碍物)for a missile or a flying saucer. The cubes are useful objects to hide behind as you can fire over them without exposing yourself to danger. The missiles will fly straight at you, but they are difficult to hit. So do not shoot at them until they are quite close. The saucers are much easier to hit, but do not chase(追逐)them as you will be open to shoot from enemy's tanks. This information is mainly about______.