must,should,ought三个词的区别与用法

问题描述:

must,should,ought三个词的区别与用法
源于
must have dropped it
should have droped it
ought to have dropped it
难得深夜还有人在,还能帮我解决疑问

1.一定已经......
2.应该已经......
3.应该已经......
(should和ought to都是“应该”之意,但后者要比前者语气要强得多 ).