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HAVE TO, NEED TO, MUST - Modal Verbs of Necessity
source: Learn English with EnglishClass101.com        2017年10月5日

How to Use 'Should', 'Ought to', 'Supposed to' and 'had better' 
source: Oxford Online English        2017年2月9日
See the full version: http://www.oxfordonlineenglish.com/sh...

How to Use 'Must' in English
source: Oxford Online English           2016年6月8日
- How to use 'must' to talk about obligations and rules.
- How to use 'mustn't' to express prohibition.
- How to use 'must' to give strong advice.
- How to use 'must' to make deductions.
- The negatives of 'must' when 'must' has different meanings.
- The past forms of 'must' in different meanings.