could combine
Regular verb: combine - combined- combined

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could combine
you could combine
he could combine
we could combine
you could combine
they could combine 	I could be combining
you could be combining
he could be combining
we could be combining
you could be combining
they could be combining	I could have combined
you could have combined
he could have combined
we could have combined
you could have combined
they could have combined	I could have been combining
you could have been combining
he could have been combining
we could have been combining
you could have been combining
they could have been combining	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could not combine
you could not combine
he could not combine
we could not combine
you could not combine
they could not combine 	I could not be combining
you could not be combining
he could not be combining
we could not be combining
you could not be combining
they could not be combining	I could not have combined
you could not have combined
he could not have combined
we could not have combined
you could not have combined
they could not have combined	I could not have been combining
you could not have been combining
he could not have been combining
we could not have been combining
you could not have been combining
they could not have been combining	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I combine?
could you combine?
could he combine?
could we combine?
could you combine?
could they combine? 	could I be combining?
could you be combining?
could he be combining?
could we be combining?
could you be combining?
could they be combining? 	could I have combined?
could you have combined?
could he have combined?
could we have combined?
could you have combined?
could they have combined? 	could I have been combining?
could you have been combining?
could he have been combining?
could we have been combining?
could you have been combining?
could they have been combining? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I not combine?
could you not combine?
could he not combine?
could we not combine?
could you not combine?
could they not combine? 	could I not be combining?
could you not be combining?
could he not be combining?
could we not be combining?
could you not be combining?
could they not be combining? 	could I not have combined?
could you not have combined?
could he not have combined?
could we not have combined?
could you not have combined?
could they not have combined? 	could I not have been combining?
could you not have been combining?
could he not have been combining?
could we not have been combining?
could you not have been combining?
could they not have been combining?