I can concentrate you can concentrate he can concentrate we can concentrate you can concentrate they can concentrate
V-ing form
I can be concentrating you can be concentrating he can be concentrating we can be concentrating you can be concentrating they can be concentrating
Perfect
I can have concentrated you can have concentrated he can have concentrated we can have concentrated you can have concentrated they can have concentrated
V-ing perfect
I can have been concentrating you can have been concentrating he can have been concentrating we can have been concentrating you can have been concentrating they can have been concentrating
Negation
Simple form
I can't concentrate you can't concentrate he can't concentrate we can't concentrate you can't concentrate they can't concentrate
V-ing form
I can't be concentrating you can't be concentrating he can't be concentrating we can't be concentrating you can't be concentrating they can't be concentrating
Perfect
I can't have concentrated you can't have concentrated he can't have concentrated we can't have concentrated you can't have concentrated they can't have concentrated
V-ing perfect
I can't have been concentrating you can't have been concentrating he can't have been concentrating we can't have been concentrating you can't have been concentrating they can't have been concentrating
Interrogative form
Simple form
can I concentrate? can you concentrate? can he concentrate? can we concentrate? can you concentrate? can they concentrate?
V-ing form
can I be concentrating? can you be concentrating? can he be concentrating? can we be concentrating? can you be concentrating? can they be concentrating?
Perfect
can I have concentrated? can you have concentrated? can he have concentrated? can we have concentrated? can you have concentrated? can they have concentrated?
V-ing perfect
can I have been concentrating? can you have been concentrating? can he have been concentrating? can we have been concentrating? can you have been concentrating? can they have been concentrating?
Interro-negative form
Simple form
can't I concentrate? can't you concentrate? can't he concentrate? can't we concentrate? can't you concentrate? can't they concentrate?
V-ing form
can't I be concentrating? can't you be concentrating? can't he be concentrating? can't we be concentrating? can't you be concentrating? can't they be concentrating?
Perfect
can't I have concentrated? can't you have concentrated? can't he have concentrated? can't we have concentrated? can't you have concentrated? can't they have concentrated?
V-ing perfect
can't I have been concentrating? can't you have been concentrating? can't he have been concentrating? can't we have been concentrating? can't you have been concentrating? can't they have been concentrating?