should flatten
Regular verb: flatten - flattened- flattened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I'd flatten
you'd flatten
she'd flatten
we'd flatten
you'd flatten
they'd flatten 	I'd be flattening
you'd be flattening
she'd be flattening
we'd be flattening
you'd be flattening
they'd be flattening	I should've flattened
you should've flattened
she should've flattened
we should've flattened
you should've flattened
they should've flattened	I should've been flattening
you should've been flattening
she should've been flattening
we should've been flattening
you should've been flattening
they should've been flattening	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I shouldn't flatten
you shouldn't flatten
she shouldn't flatten
we shouldn't flatten
you shouldn't flatten
they shouldn't flatten 	I shouldn't be flattening
you shouldn't be flattening
she shouldn't be flattening
we shouldn't be flattening
you shouldn't be flattening
they shouldn't be flattening	I shouldn't have flattened
you shouldn't have flattened
she shouldn't have flattened
we shouldn't have flattened
you shouldn't have flattened
they shouldn't have flattened	I shouldn't have been flattening
you shouldn't have been flattening
she shouldn't have been flattening
we shouldn't have been flattening
you shouldn't have been flattening
they shouldn't have been flattening	

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

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
shouldn't I flatten?
shouldn't you flatten?
shouldn't she flatten?
shouldn't we flatten?
shouldn't you flatten?
shouldn't they flatten? 	shouldn't I be flattening?
shouldn't you be flattening?
shouldn't she be flattening?
shouldn't we be flattening?
shouldn't you be flattening?
shouldn't they be flattening? 	shouldn't I have flattened?
shouldn't you have flattened?
shouldn't she have flattened?
shouldn't we have flattened?
shouldn't you have flattened?
shouldn't they have flattened? 	shouldn't I have been flattening?
shouldn't you have been flattening?
shouldn't she have been flattening?
shouldn't we have been flattening?
shouldn't you have been flattening?
shouldn't they have been flattening?