could refer
Verbo regular: refer - referred- referred

Afirmación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I could refer
you could refer
she could refer
we could refer
you could refer
they could refer 	I could be referring
you could be referring
she could be referring
we could be referring
you could be referring
they could be referring	I could have referred
you could have referred
she could have referred
we could have referred
you could have referred
they could have referred	I could have been referring
you could have been referring
she could have been referring
we could have been referring
you could have been referring
they could have been referring	

Negación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I couldn't refer
you couldn't refer
she couldn't refer
we couldn't refer
you couldn't refer
they couldn't refer 	I couldn't be referring
you couldn't be referring
she couldn't be referring
we couldn't be referring
you couldn't be referring
they couldn't be referring	I couldn't have referred
you couldn't have referred
she couldn't have referred
we couldn't have referred
you couldn't have referred
they couldn't have referred	I couldn't have been referring
you couldn't have been referring
she couldn't have been referring
we couldn't have been referring
you couldn't have been referring
they couldn't have been referring	

Forma interrogativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
could I refer?
could you refer?
could she refer?
could we refer?
could you refer?
could they refer? 	could I be referring?
could you be referring?
could she be referring?
could we be referring?
could you be referring?
could they be referring? 	could I have referred?
could you have referred?
could she have referred?
could we have referred?
could you have referred?
could they have referred? 	could I have been referring?
could you have been referring?
could she have been referring?
could we have been referring?
could you have been referring?
could they have been referring? 	

Forma interro-negativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
couldn't I refer?
couldn't you refer?
couldn't she refer?
couldn't we refer?
couldn't you refer?
couldn't they refer? 	couldn't I be referring?
couldn't you be referring?
couldn't she be referring?
couldn't we be referring?
couldn't you be referring?
couldn't they be referring? 	couldn't I have referred?
couldn't you have referred?
couldn't she have referred?
couldn't we have referred?
couldn't you have referred?
couldn't they have referred? 	couldn't I have been referring?
couldn't you have been referring?
couldn't she have been referring?
couldn't we have been referring?
couldn't you have been referring?
couldn't they have been referring?