could stack
Verbo regular: stack - stacked- stacked

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

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

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

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