must flatten
Regular verb: flatten - flattened- flattened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must flatten
you must flatten
she must flatten
we must flatten
you must flatten
they must flatten 	I must be flattening
you must be flattening
she must be flattening
we must be flattening
you must be flattening
they must be flattening	I must have flattened
you must have flattened
she must have flattened
we must have flattened
you must have flattened
they must have flattened	I must have been flattening
you must have been flattening
she must have been flattening
we must have been flattening
you must have been flattening
they must have been flattening	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't flatten
you mustn't flatten
she mustn't flatten
we mustn't flatten
you mustn't flatten
they mustn't flatten 	I mustn't be flattening
you mustn't be flattening
she mustn't be flattening
we mustn't be flattening
you mustn't be flattening
they mustn't be flattening	I mustn't have flattened
you mustn't have flattened
she mustn't have flattened
we mustn't have flattened
you mustn't have flattened
they mustn't have flattened	I mustn't have been flattening
you mustn't have been flattening
she mustn't have been flattening
we mustn't have been flattening
you mustn't have been flattening
they mustn't have been flattening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I flatten?
must you flatten?
must she flatten?
must we flatten?
must you flatten?
must they flatten? 	must I be flattening?
must you be flattening?
must she be flattening?
must we be flattening?
must you be flattening?
must they be flattening? 	must I have flattened?
must you have flattened?
must she have flattened?
must we have flattened?
must you have flattened?
must they have flattened? 	must I have been flattening?
must you have been flattening?
must she have been flattening?
must we have been flattening?
must you have been flattening?
must they have been flattening? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I flatten?
mustn't you flatten?
mustn't she flatten?
mustn't we flatten?
mustn't you flatten?
mustn't they flatten? 	mustn't I be flattening?
mustn't you be flattening?
mustn't she be flattening?
mustn't we be flattening?
mustn't you be flattening?
mustn't they be flattening? 	mustn't I have flattened?
mustn't you have flattened?
mustn't she have flattened?
mustn't we have flattened?
mustn't you have flattened?
mustn't they have flattened? 	mustn't I have been flattening?
mustn't you have been flattening?
mustn't she have been flattening?
mustn't we have been flattening?
mustn't you have been flattening?
mustn't they have been flattening?