1 、表示经常性或习惯性动作。 e.g. It seldom snows here.
2 、表示现在的特征或状态。 e.g. He is always ready to help others.
3 、普遍真理。 e.g. Action speaks louder than words.
4 、剧情图片介绍，背景说明，动作解说。 e.g. (Tom enters the room and sits at the table)
Doctor ： What's your trouble, young man?
Tom ： I've caught a cold, doctor.
