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 could not mark
you could not mark
he could not mark
we could not mark
you could not mark
they could not mark 	I could not be marking
you could not be marking
he could not be marking
we could not be marking
you could not be marking
they could not be marking	I could not have marked
you could not have marked
he could not have marked
we could not have marked
you could not have marked
they could not have marked	I could not have been marking
you could not have been marking
he could not have been marking
we could not have been marking
you could not have been marking
they could not 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 	
could I not mark?
could you not mark?
could he not mark?
could we not mark?
could you not mark?
could they not mark? 	could I not be marking?
could you not be marking?
could he not be marking?
could we not be marking?
could you not be marking?
could they not be marking? 	could I not have marked?
could you not have marked?
could he not have marked?
could we not have marked?
could you not have marked?
could they not have marked? 	could I not have been marking?
could you not have been marking?
could he not have been marking?
could we not have been marking?
could you not have been marking?
could they not have been marking?