I must crumble you must crumble she must crumble we must crumble you must crumble they must crumble
V-ing form
I must be crumbling you must be crumbling she must be crumbling we must be crumbling you must be crumbling they must be crumbling
Perfect
I must have crumbled you must have crumbled she must have crumbled we must have crumbled you must have crumbled they must have crumbled
V-ing perfect
I must have been crumbling you must have been crumbling she must have been crumbling we must have been crumbling you must have been crumbling they must have been crumbling
Negation
Simple form
I mustn't crumble you mustn't crumble she mustn't crumble we mustn't crumble you mustn't crumble they mustn't crumble
V-ing form
I mustn't be crumbling you mustn't be crumbling she mustn't be crumbling we mustn't be crumbling you mustn't be crumbling they mustn't be crumbling
Perfect
I mustn't have crumbled you mustn't have crumbled she mustn't have crumbled we mustn't have crumbled you mustn't have crumbled they mustn't have crumbled
V-ing perfect
I mustn't have been crumbling you mustn't have been crumbling she mustn't have been crumbling we mustn't have been crumbling you mustn't have been crumbling they mustn't have been crumbling
Interrogative form
Simple form
must I crumble? must you crumble? must she crumble? must we crumble? must you crumble? must they crumble?
V-ing form
must I be crumbling? must you be crumbling? must she be crumbling? must we be crumbling? must you be crumbling? must they be crumbling?
Perfect
must I have crumbled? must you have crumbled? must she have crumbled? must we have crumbled? must you have crumbled? must they have crumbled?
V-ing perfect
must I have been crumbling? must you have been crumbling? must she have been crumbling? must we have been crumbling? must you have been crumbling? must they have been crumbling?
Interro-negative form
Simple form
mustn't I crumble? mustn't you crumble? mustn't she crumble? mustn't we crumble? mustn't you crumble? mustn't they crumble?
V-ing form
mustn't I be crumbling? mustn't you be crumbling? mustn't she be crumbling? mustn't we be crumbling? mustn't you be crumbling? mustn't they be crumbling?
Perfect
mustn't I have crumbled? mustn't you have crumbled? mustn't she have crumbled? mustn't we have crumbled? mustn't you have crumbled? mustn't they have crumbled?
V-ing perfect
mustn't I have been crumbling? mustn't you have been crumbling? mustn't she have been crumbling? mustn't we have been crumbling? mustn't you have been crumbling? mustn't they have been crumbling?