I can combine you can combine he can combine we can combine you can combine they can combine
V-ing form
I can be combining you can be combining he can be combining we can be combining you can be combining they can be combining
Perfect
I can have combined you can have combined he can have combined we can have combined you can have combined they can have combined
V-ing perfect
I can have been combining you can have been combining he can have been combining we can have been combining you can have been combining they can have been combining
Negation
Simple form
I can't combine you can't combine he can't combine we can't combine you can't combine they can't combine
V-ing form
I can't be combining you can't be combining he can't be combining we can't be combining you can't be combining they can't be combining
Perfect
I can't have combined you can't have combined he can't have combined we can't have combined you can't have combined they can't have combined
V-ing perfect
I can't have been combining you can't have been combining he can't have been combining we can't have been combining you can't have been combining they can't have been combining
Interrogative form
Simple form
can I combine? can you combine? can he combine? can we combine? can you combine? can they combine?
V-ing form
can I be combining? can you be combining? can he be combining? can we be combining? can you be combining? can they be combining?
Perfect
can I have combined? can you have combined? can he have combined? can we have combined? can you have combined? can they have combined?
V-ing perfect
can I have been combining? can you have been combining? can he have been combining? can we have been combining? can you have been combining? can they have been combining?
Interro-negative form
Simple form
can't I combine? can't you combine? can't he combine? can't we combine? can't you combine? can't they combine?
V-ing form
can't I be combining? can't you be combining? can't he be combining? can't we be combining? can't you be combining? can't they be combining?
Perfect
can't I have combined? can't you have combined? can't he have combined? can't we have combined? can't you have combined? can't they have combined?
V-ing perfect
can't I have been combining? can't you have been combining? can't he have been combining? can't we have been combining? can't you have been combining? can't they have been combining?