I could prolong you could prolong he could prolong we could prolong you could prolong they could prolong
V-ing form
I could be prolonging you could be prolonging he could be prolonging we could be prolonging you could be prolonging they could be prolonging
Perfect
I could have prolonged you could have prolonged he could have prolonged we could have prolonged you could have prolonged they could have prolonged
V-ing perfect
I could have been prolonging you could have been prolonging he could have been prolonging we could have been prolonging you could have been prolonging they could have been prolonging
Negation
Simple form
I could not prolong you could not prolong he could not prolong we could not prolong you could not prolong they could not prolong
V-ing form
I could not be prolonging you could not be prolonging he could not be prolonging we could not be prolonging you could not be prolonging they could not be prolonging
Perfect
I could not have prolonged you could not have prolonged he could not have prolonged we could not have prolonged you could not have prolonged they could not have prolonged
V-ing perfect
I could not have been prolonging you could not have been prolonging he could not have been prolonging we could not have been prolonging you could not have been prolonging they could not have been prolonging
Interrogative form
Simple form
could I prolong? could you prolong? could he prolong? could we prolong? could you prolong? could they prolong?
V-ing form
could I be prolonging? could you be prolonging? could he be prolonging? could we be prolonging? could you be prolonging? could they be prolonging?
Perfect
could I have prolonged? could you have prolonged? could he have prolonged? could we have prolonged? could you have prolonged? could they have prolonged?
V-ing perfect
could I have been prolonging? could you have been prolonging? could he have been prolonging? could we have been prolonging? could you have been prolonging? could they have been prolonging?
Interro-negative form
Simple form
could I not prolong? could you not prolong? could he not prolong? could we not prolong? could you not prolong? could they not prolong?
V-ing form
could I not be prolonging? could you not be prolonging? could he not be prolonging? could we not be prolonging? could you not be prolonging? could they not be prolonging?
Perfect
could I not have prolonged? could you not have prolonged? could he not have prolonged? could we not have prolonged? could you not have prolonged? could they not have prolonged?
V-ing perfect
could I not have been prolonging? could you not have been prolonging? could he not have been prolonging? could we not have been prolonging? could you not have been prolonging? could they not have been prolonging?