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 could not question you could not question he could not question we could not question you could not question they could not question
V-ing form
I could not be questioning you could not be questioning he could not be questioning we could not be questioning you could not be questioning they could not be questioning
Perfect
I could not have questioned you could not have questioned he could not have questioned we could not have questioned you could not have questioned they could not have questioned
V-ing perfect
I could not have been questioning you could not have been questioning he could not have been questioning we could not have been questioning you could not have been questioning they could not 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
could I not question? could you not question? could he not question? could we not question? could you not question? could they not question?
V-ing form
could I not be questioning? could you not be questioning? could he not be questioning? could we not be questioning? could you not be questioning? could they not be questioning?
Perfect
could I not have questioned? could you not have questioned? could he not have questioned? could we not have questioned? could you not have questioned? could they not have questioned?
V-ing perfect
could I not have been questioning? could you not have been questioning? could he not have been questioning? could we not have been questioning? could you not have been questioning? could they not have been questioning?