could concentrate
Verbo regular: concentrate - concentrated- concentrated

Afirmación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I could concentrate
you could concentrate
he could concentrate
we could concentrate
you could concentrate
they could concentrate 	I could be concentrating
you could be concentrating
he could be concentrating
we could be concentrating
you could be concentrating
they could be concentrating	I could have concentrated
you could have concentrated
he could have concentrated
we could have concentrated
you could have concentrated
they could have concentrated	I could have been concentrating
you could have been concentrating
he could have been concentrating
we could have been concentrating
you could have been concentrating
they could have been concentrating	

Negación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I couldn't concentrate
you couldn't concentrate
he couldn't concentrate
we couldn't concentrate
you couldn't concentrate
they couldn't concentrate 	I couldn't be concentrating
you couldn't be concentrating
he couldn't be concentrating
we couldn't be concentrating
you couldn't be concentrating
they couldn't be concentrating	I couldn't have concentrated
you couldn't have concentrated
he couldn't have concentrated
we couldn't have concentrated
you couldn't have concentrated
they couldn't have concentrated	I couldn't have been concentrating
you couldn't have been concentrating
he couldn't have been concentrating
we couldn't have been concentrating
you couldn't have been concentrating
they couldn't have been concentrating	

Forma interrogativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
could I concentrate?
could you concentrate?
could he concentrate?
could we concentrate?
could you concentrate?
could they concentrate? 	could I be concentrating?
could you be concentrating?
could he be concentrating?
could we be concentrating?
could you be concentrating?
could they be concentrating? 	could I have concentrated?
could you have concentrated?
could he have concentrated?
could we have concentrated?
could you have concentrated?
could they have concentrated? 	could I have been concentrating?
could you have been concentrating?
could he have been concentrating?
could we have been concentrating?
could you have been concentrating?
could they have been concentrating? 	

Forma interro-negativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
couldn't I concentrate?
couldn't you concentrate?
couldn't he concentrate?
couldn't we concentrate?
couldn't you concentrate?
couldn't they concentrate? 	couldn't I be concentrating?
couldn't you be concentrating?
couldn't he be concentrating?
couldn't we be concentrating?
couldn't you be concentrating?
couldn't they be concentrating? 	couldn't I have concentrated?
couldn't you have concentrated?
couldn't he have concentrated?
couldn't we have concentrated?
couldn't you have concentrated?
couldn't they have concentrated? 	couldn't I have been concentrating?
couldn't you have been concentrating?
couldn't he have been concentrating?
couldn't we have been concentrating?
couldn't you have been concentrating?
couldn't they have been concentrating?