could mark
Regular verb: mark - marked- marked

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could mark
you could mark
he could mark
we could mark
you could mark
they could mark 	I could be marking
you could be marking
he could be marking
we could be marking
you could be marking
they could be marking	I could have marked
you could have marked
he could have marked
we could have marked
you could have marked
they could have marked	I could have been marking
you could have been marking
he could have been marking
we could have been marking
you could have been marking
they could have been marking	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't mark
you couldn't mark
he couldn't mark
we couldn't mark
you couldn't mark
they couldn't mark 	I couldn't be marking
you couldn't be marking
he couldn't be marking
we couldn't be marking
you couldn't be marking
they couldn't be marking	I couldn't have marked
you couldn't have marked
he couldn't have marked
we couldn't have marked
you couldn't have marked
they couldn't have marked	I couldn't have been marking
you couldn't have been marking
he couldn't have been marking
we couldn't have been marking
you couldn't have been marking
they couldn't have been marking	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I mark?
could you mark?
could he mark?
could we mark?
could you mark?
could they mark? 	could I be marking?
could you be marking?
could he be marking?
could we be marking?
could you be marking?
could they be marking? 	could I have marked?
could you have marked?
could he have marked?
could we have marked?
could you have marked?
could they have marked? 	could I have been marking?
could you have been marking?
could he have been marking?
could we have been marking?
could you have been marking?
could they have been marking? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I mark?
couldn't you mark?
couldn't he mark?
couldn't we mark?
couldn't you mark?
couldn't they mark? 	couldn't I be marking?
couldn't you be marking?
couldn't he be marking?
couldn't we be marking?
couldn't you be marking?
couldn't they be marking? 	couldn't I have marked?
couldn't you have marked?
couldn't he have marked?
couldn't we have marked?
couldn't you have marked?
couldn't they have marked? 	couldn't I have been marking?
couldn't you have been marking?
couldn't he have been marking?
couldn't we have been marking?
couldn't you have been marking?
couldn't they have been marking?