must lengthen
Verbo regular: lengthen - lengthened- lengthened

Afirmación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I must lengthen
you must lengthen
she must lengthen
we must lengthen
you must lengthen
they must lengthen 	I must be lengthening
you must be lengthening
she must be lengthening
we must be lengthening
you must be lengthening
they must be lengthening	I must have lengthened
you must have lengthened
she must have lengthened
we must have lengthened
you must have lengthened
they must have lengthened	I must have been lengthening
you must have been lengthening
she must have been lengthening
we must have been lengthening
you must have been lengthening
they must have been lengthening	

Negación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I mustn't lengthen
you mustn't lengthen
she mustn't lengthen
we mustn't lengthen
you mustn't lengthen
they mustn't lengthen 	I mustn't be lengthening
you mustn't be lengthening
she mustn't be lengthening
we mustn't be lengthening
you mustn't be lengthening
they mustn't be lengthening	I mustn't have lengthened
you mustn't have lengthened
she mustn't have lengthened
we mustn't have lengthened
you mustn't have lengthened
they mustn't have lengthened	I mustn't have been lengthening
you mustn't have been lengthening
she mustn't have been lengthening
we mustn't have been lengthening
you mustn't have been lengthening
they mustn't have been lengthening	

Forma interrogativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
must I lengthen?
must you lengthen?
must she lengthen?
must we lengthen?
must you lengthen?
must they lengthen? 	must I be lengthening?
must you be lengthening?
must she be lengthening?
must we be lengthening?
must you be lengthening?
must they be lengthening? 	must I have lengthened?
must you have lengthened?
must she have lengthened?
must we have lengthened?
must you have lengthened?
must they have lengthened? 	must I have been lengthening?
must you have been lengthening?
must she have been lengthening?
must we have been lengthening?
must you have been lengthening?
must they have been lengthening? 	

Forma interro-negativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
mustn't I lengthen?
mustn't you lengthen?
mustn't she lengthen?
mustn't we lengthen?
mustn't you lengthen?
mustn't they lengthen? 	mustn't I be lengthening?
mustn't you be lengthening?
mustn't she be lengthening?
mustn't we be lengthening?
mustn't you be lengthening?
mustn't they be lengthening? 	mustn't I have lengthened?
mustn't you have lengthened?
mustn't she have lengthened?
mustn't we have lengthened?
mustn't you have lengthened?
mustn't they have lengthened? 	mustn't I have been lengthening?
mustn't you have been lengthening?
mustn't she have been lengthening?
mustn't we have been lengthening?
mustn't you have been lengthening?
mustn't they have been lengthening?