forth adv.向前，向外
例句：It will move horizontally back and forth at the bottom of the screen, shooting bullets upwards. Your ship will be controlled by, say, the keyboard.
句意：在这个游戏中，您将通过键盘来控制一个宇宙飞船，它可以在屏幕底端水平向前或向后移动，还可以向上发射子弹。