last 表示“最后”,则不用加for,如果是表示“持续多少时间”则要加for,
例如：
持续了3天：last for 3days.但是我在字典里查到 Each lesson lasts an hour.The ceasefire doesn't last long.那么，这又是怎么回事了？Last for 表示持续一段时间，复数，请看例句：The sale was supposed to last for a week, but for all practical purposes it's over. 减价销售原来预料要持续一周，然而实际上已经结束了。 The blockade is likely to last for some time. 封锁可能要持续一段时间。 This medicine will lastfor a time,but after six months you'll need a booster. 这种药的效力可维持一段时期，但6个月后就需要使用增强药效的辅助剂。The ceasefire doesn't last long.这里last 没有加for是因为具体多久时间不确定。