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