could concentrate
Regular verb: concentrate - concentrated- concentrated

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
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	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could not concentrate
you could not concentrate
he could not concentrate
we could not concentrate
you could not concentrate
they could not concentrate 	I could not be concentrating
you could not be concentrating
he could not be concentrating
we could not be concentrating
you could not be concentrating
they could not be concentrating	I could not have concentrated
you could not have concentrated
he could not have concentrated
we could not have concentrated
you could not have concentrated
they could not have concentrated	I could not have been concentrating
you could not have been concentrating
he could not have been concentrating
we could not have been concentrating
you could not have been concentrating
they could not have been concentrating	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
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? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I not concentrate?
could you not concentrate?
could he not concentrate?
could we not concentrate?
could you not concentrate?
could they not concentrate? 	could I not be concentrating?
could you not be concentrating?
could he not be concentrating?
could we not be concentrating?
could you not be concentrating?
could they not be concentrating? 	could I not have concentrated?
could you not have concentrated?
could he not have concentrated?
could we not have concentrated?
could you not have concentrated?
could they not have concentrated? 	could I not have been concentrating?
could you not have been concentrating?
could he not have been concentrating?
could we not have been concentrating?
could you not have been concentrating?
could they not have been concentrating?