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 cannot concentrate you cannot concentrate he cannot concentrate we cannot concentrate you cannot concentrate they cannot concentrate
V-ing form
I cannot be concentrating you cannot be concentrating he cannot be concentrating we cannot be concentrating you cannot be concentrating they cannot be concentrating
Perfect
I cannot have concentrated you cannot have concentrated he cannot have concentrated we cannot have concentrated you cannot have concentrated they cannot have concentrated
V-ing perfect
I cannot have been concentrating you cannot have been concentrating he cannot have been concentrating we cannot have been concentrating you cannot have been concentrating they cannot 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 I not concentrate? can you not concentrate? can he not concentrate? can we not concentrate? can you not concentrate? can they not concentrate?
V-ing form
can I not be concentrating? can you not be concentrating? can he not be concentrating? can we not be concentrating? can you not be concentrating? can they not be concentrating?
Perfect
can I not have concentrated? can you not have concentrated? can he not have concentrated? can we not have concentrated? can you not have concentrated? can they not have concentrated?
V-ing perfect
can I not have been concentrating? can you not have been concentrating? can he not have been concentrating? can we not have been concentrating? can you not have been concentrating? can they not have been concentrating?