must stack
Regular verb: stack - stacked- stacked

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must stack
you must stack
she must stack
we must stack
you must stack
they must stack 	I must be stacking
you must be stacking
she must be stacking
we must be stacking
you must be stacking
they must be stacking	I must have stacked
you must have stacked
she 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
she must have been stacking
we must have been stacking
you must have been stacking
they must have been stacking	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't stack
you mustn't stack
she 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
she 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
she 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
she mustn't have been stacking
we mustn't have been stacking
you mustn't have been stacking
they mustn't have been stacking	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I stack?
must you stack?
must she stack?
must we stack?
must you stack?
must they stack? 	must I be stacking?
must you be stacking?
must she be stacking?
must we be stacking?
must you be stacking?
must they be stacking? 	must I have stacked?
must you have stacked?
must she 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 she have been stacking?
must we have been stacking?
must you have been stacking?
must they have been stacking? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I stack?
mustn't you stack?
mustn't she 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 she 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 she 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 she have been stacking?
mustn't we have been stacking?
mustn't you have been stacking?
mustn't they have been stacking?