I could question you could question he could question we could question you could question they could question
V-ing form
I could be questioning you could be questioning he could be questioning we could be questioning you could be questioning they could be questioning
Perfect
I could have questioned you could have questioned he could have questioned we could have questioned you could have questioned they could have questioned
V-ing perfect
I could have been questioning you could have been questioning he could have been questioning we could have been questioning you could have been questioning they could have been questioning
Negation
Simple form
I couldn't question you couldn't question he couldn't question we couldn't question you couldn't question they couldn't question
V-ing form
I couldn't be questioning you couldn't be questioning he couldn't be questioning we couldn't be questioning you couldn't be questioning they couldn't be questioning
Perfect
I couldn't have questioned you couldn't have questioned he couldn't have questioned we couldn't have questioned you couldn't have questioned they couldn't have questioned
V-ing perfect
I couldn't have been questioning you couldn't have been questioning he couldn't have been questioning we couldn't have been questioning you couldn't have been questioning they couldn't have been questioning
Interrogative form
Simple form
could I question? could you question? could he question? could we question? could you question? could they question?
V-ing form
could I be questioning? could you be questioning? could he be questioning? could we be questioning? could you be questioning? could they be questioning?
Perfect
could I have questioned? could you have questioned? could he have questioned? could we have questioned? could you have questioned? could they have questioned?
V-ing perfect
could I have been questioning? could you have been questioning? could he have been questioning? could we have been questioning? could you have been questioning? could they have been questioning?
Interro-negative form
Simple form
couldn't I question? couldn't you question? couldn't he question? couldn't we question? couldn't you question? couldn't they question?
V-ing form
couldn't I be questioning? couldn't you be questioning? couldn't he be questioning? couldn't we be questioning? couldn't you be questioning? couldn't they be questioning?
Perfect
couldn't I have questioned? couldn't you have questioned? couldn't he have questioned? couldn't we have questioned? couldn't you have questioned? couldn't they have questioned?
V-ing perfect
couldn't I have been questioning? couldn't you have been questioning? couldn't he have been questioning? couldn't we have been questioning? couldn't you have been questioning? couldn't they have been questioning?