could flatten
Regular verb: flatten - flattened- flattened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could flatten
you could flatten
he could flatten
we could flatten
you could flatten
they could flatten 	I could be flattening
you could be flattening
he could be flattening
we could be flattening
you could be flattening
they could be flattening	I could have flattened
you could have flattened
he could have flattened
we could have flattened
you could have flattened
they could have flattened	I could have been flattening
you could have been flattening
he could have been flattening
we could have been flattening
you could have been flattening
they could have been flattening	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could not flatten
you could not flatten
he could not flatten
we could not flatten
you could not flatten
they could not flatten 	I could not be flattening
you could not be flattening
he could not be flattening
we could not be flattening
you could not be flattening
they could not be flattening	I could not have flattened
you could not have flattened
he could not have flattened
we could not have flattened
you could not have flattened
they could not have flattened	I could not have been flattening
you could not have been flattening
he could not have been flattening
we could not have been flattening
you could not have been flattening
they could not have been flattening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I flatten?
could you flatten?
could he flatten?
could we flatten?
could you flatten?
could they flatten? 	could I be flattening?
could you be flattening?
could he be flattening?
could we be flattening?
could you be flattening?
could they be flattening? 	could I have flattened?
could you have flattened?
could he have flattened?
could we have flattened?
could you have flattened?
could they have flattened? 	could I have been flattening?
could you have been flattening?
could he have been flattening?
could we have been flattening?
could you have been flattening?
could they have been flattening? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I not flatten?
could you not flatten?
could he not flatten?
could we not flatten?
could you not flatten?
could they not flatten? 	could I not be flattening?
could you not be flattening?
could he not be flattening?
could we not be flattening?
could you not be flattening?
could they not be flattening? 	could I not have flattened?
could you not have flattened?
could he not have flattened?
could we not have flattened?
could you not have flattened?
could they not have flattened? 	could I not have been flattening?
could you not have been flattening?
could he not have been flattening?
could we not have been flattening?
could you not have been flattening?
could they not have been flattening?