You can use constant, continual, and continuous to describe things that happen or exist without stopping. You describe something as constant when it happens all the time or never goes away. He was in constant pain. ...Eva's constant criticism. Continual is usually used to describe something that happens often over a period of time, especially something undesirable. ...his continual drinking. ...continual demands to cut costs. If something is continuous, it happens all the time without stopping, or seems to do so. ...days of continuous rain. ...a continuous background noise.

constant, continual 和 continuous 均可用来描述不断发生或一直存在的事物。constant 表示一直在发生或从未消失：He was in constant pain (他的疼痛一直没有消停)，Eva's constant criticism (伊娃没完没了的批评)。continual 通常用来形容一段时期内经常发生的事，尤其是令人讨厌的事：his continual drinking (他经常饮酒)，continual demands to cut costs (不断要求削减成本)。continuous 表示一直没有间断，或者貌似如此：days of continuous rain (淫雨霏霏的日子)，a continuous background noise (持续不断的背景噪音)。