从肯定到否定：（肯定的程度由高到低到否定）must,should,may(偶尔也会用can但不太常用,因为一般用于否定或疑问了),might,can't对现在的推测：must/should/may/might/can't +动词原形对已发生的动作或状态的推测：mu...