English verb conjugation
COULD CONCENTRATE

Regular verb: concentrate - concentrated - concentrated

Affirmation

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

Interrogative form

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