English verb conjugation
COULD MARK

Regular verb: mark - marked - marked

Affirmation

Simple form	V-ing form
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
Perfect	V-ing perfect
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
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
Perfect	V-ing perfect
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
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?
Perfect	V-ing perfect
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
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?
Perfect	V-ing perfect
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?