could fasten
Verbo regular: fasten - fastened- fastened

Afirmación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I could fasten
you could fasten
she could fasten
we could fasten
you could fasten
they could fasten 	I could be fastening
you could be fastening
she could be fastening
we could be fastening
you could be fastening
they could be fastening	I could have fastened
you could have fastened
she could have fastened
we could have fastened
you could have fastened
they could have fastened	I could have been fastening
you could have been fastening
she could have been fastening
we could have been fastening
you could have been fastening
they could have been fastening	

Negación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I couldn't fasten
you couldn't fasten
she couldn't fasten
we couldn't fasten
you couldn't fasten
they couldn't fasten 	I couldn't be fastening
you couldn't be fastening
she couldn't be fastening
we couldn't be fastening
you couldn't be fastening
they couldn't be fastening	I couldn't have fastened
you couldn't have fastened
she couldn't have fastened
we couldn't have fastened
you couldn't have fastened
they couldn't have fastened	I couldn't have been fastening
you couldn't have been fastening
she couldn't have been fastening
we couldn't have been fastening
you couldn't have been fastening
they couldn't have been fastening	

Forma interrogativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
could I fasten?
could you fasten?
could she fasten?
could we fasten?
could you fasten?
could they fasten? 	could I be fastening?
could you be fastening?
could she be fastening?
could we be fastening?
could you be fastening?
could they be fastening? 	could I have fastened?
could you have fastened?
could she have fastened?
could we have fastened?
could you have fastened?
could they have fastened? 	could I have been fastening?
could you have been fastening?
could she have been fastening?
could we have been fastening?
could you have been fastening?
could they have been fastening? 	

Forma interro-negativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
couldn't I fasten?
couldn't you fasten?
couldn't she fasten?
couldn't we fasten?
couldn't you fasten?
couldn't they fasten? 	couldn't I be fastening?
couldn't you be fastening?
couldn't she be fastening?
couldn't we be fastening?
couldn't you be fastening?
couldn't they be fastening? 	couldn't I have fastened?
couldn't you have fastened?
couldn't she have fastened?
couldn't we have fastened?
couldn't you have fastened?
couldn't they have fastened? 	couldn't I have been fastening?
couldn't you have been fastening?
couldn't she have been fastening?
couldn't we have been fastening?
couldn't you have been fastening?
couldn't they have been fastening?