must stack
Verbo regular: stack - stacked- stacked

Afirmación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I must stack
you must stack
he must stack
we must stack
you must stack
they must stack 	I must be stacking
you must be stacking
he must be stacking
we must be stacking
you must be stacking
they must be stacking	I must have stacked
you must have stacked
he must have stacked
we must have stacked
you must have stacked
they must have stacked	I must have been stacking
you must have been stacking
he must have been stacking
we must have been stacking
you must have been stacking
they must have been stacking	

Negación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I mustn't stack
you mustn't stack
he mustn't stack
we mustn't stack
you mustn't stack
they mustn't stack 	I mustn't be stacking
you mustn't be stacking
he mustn't be stacking
we mustn't be stacking
you mustn't be stacking
they mustn't be stacking	I mustn't have stacked
you mustn't have stacked
he mustn't have stacked
we mustn't have stacked
you mustn't have stacked
they mustn't have stacked	I mustn't have been stacking
you mustn't have been stacking
he mustn't have been stacking
we mustn't have been stacking
you mustn't have been stacking
they mustn't have been stacking	

Forma interrogativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
must I stack?
must you stack?
must he stack?
must we stack?
must you stack?
must they stack? 	must I be stacking?
must you be stacking?
must he be stacking?
must we be stacking?
must you be stacking?
must they be stacking? 	must I have stacked?
must you have stacked?
must he have stacked?
must we have stacked?
must you have stacked?
must they have stacked? 	must I have been stacking?
must you have been stacking?
must he have been stacking?
must we have been stacking?
must you have been stacking?
must they have been stacking? 	

Forma interro-negativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
mustn't I stack?
mustn't you stack?
mustn't he stack?
mustn't we stack?
mustn't you stack?
mustn't they stack? 	mustn't I be stacking?
mustn't you be stacking?
mustn't he be stacking?
mustn't we be stacking?
mustn't you be stacking?
mustn't they be stacking? 	mustn't I have stacked?
mustn't you have stacked?
mustn't he have stacked?
mustn't we have stacked?
mustn't you have stacked?
mustn't they have stacked? 	mustn't I have been stacking?
mustn't you have been stacking?
mustn't he have been stacking?
mustn't we have been stacking?
mustn't you have been stacking?
mustn't they have been stacking?