have to,must ,gotta的区别?用法!

1. have to是表示不得不要,大多是因为客观方面的原因.例:i have to go because it's time for school now.

2. must也是"不得不"的意思,但客观原因方面比较弱.

3. gotta=have got to)必须,俚语,较不正式